diff --git a/api/mixins.py b/api/mixins.py
deleted file mode 100644
index c5266da88..000000000
--- a/api/mixins.py
+++ /dev/null
@@ -1,29 +0,0 @@
-# -*- coding: utf-8 -*-
-from collections import OrderedDict
-
-from rest_framework.response import Response
-
-
-class TimerFieldSupportMixin:
-    def options(self, request, *args, **kwargs):
-        """
-        Add information about the optional "timer" field.
-        """
-        meta = self.metadata_class()
-        data = meta.determine_metadata(request, self)
-        post = data.get("actions").get("POST")  # type: OrderedDict
-        post["timer"] = OrderedDict(
-            {
-                "type": "integer",
-                "required": False,
-                "read_only": False,
-                "label": "Timer",
-                "details": "ID for an existing Timer, may be used in place of the "
-                "`start`, `end`, and/or `child` fields. ",
-            }
-        )
-        details = "Required unless a value is provided in the `timer` field."
-        post["child"]["details"] = details
-        post["start"]["details"] = details
-        post["end"]["details"] = details
-        return Response(data)
diff --git a/api/serializers.py b/api/serializers.py
index 9c3314fc7..19013ea4b 100644
--- a/api/serializers.py
+++ b/api/serializers.py
@@ -39,16 +39,30 @@ class CoreModelWithDurationSerializer(CoreModelSerializer):
 
     child = serializers.PrimaryKeyRelatedField(
         allow_null=True,
-        allow_empty=True,
+        help_text="Required unless a Timer value is provided.",
         queryset=models.Child.objects.all(),
         required=False,
     )
 
+    timer = serializers.PrimaryKeyRelatedField(
+        allow_null=True,
+        help_text="May be used in place of the Start, End, and/or Child values.",
+        queryset=models.Timer.objects.all(),
+        required=False,
+        write_only=True,
+    )
+
     class Meta:
         abstract = True
         extra_kwargs = {
-            "start": {"required": False},
-            "end": {"required": False},
+            "start": {
+                "help_text": "Required unless a Timer value is provided.",
+                "required": False,
+            },
+            "end": {
+                "help_text": "Required unless a Timer value is provided.",
+                "required": False,
+            },
         }
 
     def validate(self, attrs):
@@ -56,11 +70,12 @@ def validate(self, attrs):
         # of "start" and "end" fields as well as "child" if it is set on the
         # Timer entry.
         timer = None
-        if "timer" in self.initial_data:
-            try:
-                timer = models.Timer.objects.get(pk=self.initial_data["timer"])
-            except models.Timer.DoesNotExist:
-                raise ValidationError({"timer": ["Timer does not exist."]})
+        if "timer" in attrs:
+            # Remove the "timer" attribute (super validation would fail as it
+            # is not a true field on the model).
+            timer = attrs["timer"]
+            attrs.pop("timer")
+
             if timer.end:
                 end = timer.end
             else:
@@ -142,6 +157,7 @@ class Meta(CoreModelWithDurationSerializer.Meta):
             "child",
             "start",
             "end",
+            "timer",
             "duration",
             "type",
             "method",
@@ -172,7 +188,17 @@ class Meta:
 class SleepSerializer(CoreModelWithDurationSerializer, TaggableSerializer):
     class Meta(CoreModelWithDurationSerializer.Meta):
         model = models.Sleep
-        fields = ("id", "child", "start", "end", "duration", "nap", "notes", "tags")
+        fields = (
+            "id",
+            "child",
+            "start",
+            "end",
+            "timer",
+            "duration",
+            "nap",
+            "notes",
+            "tags",
+        )
 
 
 class TagSerializer(serializers.HyperlinkedModelSerializer):
@@ -220,7 +246,16 @@ def validate(self, attrs):
 class TummyTimeSerializer(CoreModelWithDurationSerializer, TaggableSerializer):
     class Meta(CoreModelWithDurationSerializer.Meta):
         model = models.TummyTime
-        fields = ("id", "child", "start", "end", "duration", "milestone", "tags")
+        fields = (
+            "id",
+            "child",
+            "start",
+            "end",
+            "timer",
+            "duration",
+            "milestone",
+            "tags",
+        )
 
 
 class UserSerializer(serializers.ModelSerializer):
diff --git a/api/views.py b/api/views.py
index 80e5e28ea..3a7964cf0 100644
--- a/api/views.py
+++ b/api/views.py
@@ -6,7 +6,6 @@
 from core import models
 
 from . import serializers, filters
-from .mixins import TimerFieldSupportMixin
 
 
 class BMIViewSet(viewsets.ModelViewSet):
@@ -37,7 +36,7 @@ class DiaperChangeViewSet(viewsets.ModelViewSet):
     filterset_class = filters.DiaperChangeFilter
 
 
-class FeedingViewSet(TimerFieldSupportMixin, viewsets.ModelViewSet):
+class FeedingViewSet(viewsets.ModelViewSet):
     queryset = models.Feeding.objects.all()
     serializer_class = serializers.FeedingSerializer
     filterset_class = filters.FeedingFilter
@@ -67,7 +66,7 @@ class PumpingViewSet(viewsets.ModelViewSet):
     filterset_class = filters.PumpingFilter
 
 
-class SleepViewSet(TimerFieldSupportMixin, viewsets.ModelViewSet):
+class SleepViewSet(viewsets.ModelViewSet):
     queryset = models.Sleep.objects.all()
     serializer_class = serializers.SleepSerializer
     filterset_class = filters.SleepFilter
@@ -104,7 +103,7 @@ def restart(self, request, pk=None):
         return Response(self.serializer_class(timer).data)
 
 
-class TummyTimeViewSet(TimerFieldSupportMixin, viewsets.ModelViewSet):
+class TummyTimeViewSet(viewsets.ModelViewSet):
     queryset = models.TummyTime.objects.all()
     serializer_class = serializers.TummyTimeSerializer
     filterset_class = filters.TummyTimeFilter
diff --git a/openapi-schema.yml b/openapi-schema.yml
index b3fb719c3..fdd255997 100644
--- a/openapi-schema.yml
+++ b/openapi-schema.yml
@@ -4684,12 +4684,20 @@ components:
         child:
           type: integer
           nullable: true
+          description: Required unless a Timer value is provided.
         start:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
         end:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
+        timer:
+          type: integer
+          writeOnly: true
+          nullable: true
+          description: May be used in place of the Start, End, and/or Child values.
         duration:
           type: string
           readOnly: true
@@ -4809,12 +4817,20 @@ components:
         child:
           type: integer
           nullable: true
+          description: Required unless a Timer value is provided.
         start:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
         end:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
+        timer:
+          type: integer
+          writeOnly: true
+          nullable: true
+          description: May be used in place of the Start, End, and/or Child values.
         duration:
           type: string
           readOnly: true
@@ -4905,12 +4921,20 @@ components:
         child:
           type: integer
           nullable: true
+          description: Required unless a Timer value is provided.
         start:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
         end:
           type: string
           format: date-time
+          description: Required unless a Timer value is provided.
+        timer:
+          type: integer
+          writeOnly: true
+          nullable: true
+          description: May be used in place of the Start, End, and/or Child values.
         duration:
           type: string
           readOnly: true