Proposed handling of intervals in seconds.

Rejects when a job's interval is lower than a queue's interval.
Rejects when a job's interval is not a multiple of a queue's interval. This seemed to be the most restrictive approach from which things can be loosened up.
Added a settings parameter DJANGO_RQ_SCHEDULER_INTERVAL that can be used to change the schedular interval. Default is 60 matching DJANGO_RQ's default.
Renamed migration adding seconds to be more descriptive.

scheduler/models.py

@@ -16,6 +16,9 @@
 from model_utils.models import TimeStampedModel
 
 
+RQ_SCHEDULER_INTERVAL = getattr(settings, "DJANGO_RQ_SCHEDULER_INTERVAL", 60)
+
+
 @python_2_unicode_compatible
 class BaseJob(TimeStampedModel):
 
@@ -90,7 +93,7 @@ def delete(self, **kwargs):
         super(BaseJob, self).delete(**kwargs)
 
     def scheduler(self):
-        return django_rq.get_scheduler(self.queue)
+        return django_rq.get_scheduler(self.queue, interval=RQ_SCHEDULER_INTERVAL)
 
     def is_schedulable(self):
         if self.job_id:
@@ -160,6 +163,20 @@ class RepeatableJob(ScheduledTimeMixin, BaseJob):
     )
     repeat = models.PositiveIntegerField(_('repeat'), blank=True, null=True)
 
+    def clean(self):
+        super(RepeatableJob, self).clean()
+        self.clean_interval_unit()
+
+    def clean_interval_unit(self):
+        if RQ_SCHEDULER_INTERVAL > self.interval_seconds():
+            raise ValidationError({
+                'interval_unit': ValidationError(
+                    _("Job interval is set lower than {} queue's interval.".format(self.queue)), code='invalid')
+            })
+        if self.interval_seconds() % RQ_SCHEDULER_INTERVAL:
+            raise ValidationError(_("Job interval is not a multiple of rq_scheduler's interval frequency: {}s".format(
+                        RQ_SCHEDULER_INTERVAL)), code='invalid')
+
     def interval_display(self):
         return '{} {}'.format(self.interval, self.get_interval_unit_display())
 

scheduler/tests.py

@@ -209,6 +209,39 @@ class TestRepeatableJob(TestScheduledJob):
     JobClass = RepeatableJob
     JobClassFactory = RepeatableJobFactory
 
+    def test_clean(self):
+        job = self.JobClass()
+        job.queue = list(settings.RQ_QUEUES)[0]
+        job.callable = 'scheduler.tests.test_job'
+        job.interval = 1
+        assert job.clean() is None
+
+    def test_clean_seconds(self):
+        job = self.JobClass()
+        job.queue = list(settings.RQ_QUEUES)[0]
+        job.callable = 'scheduler.tests.test_job'
+        job.interval = 60
+        job.interval_unit = 'seconds'
+        assert job.clean() is None
+
+    def test_clean_too_frequent(self):
+        job = self.JobClass()
+        job.queue = list(settings.RQ_QUEUES)[0]
+        job.callable = 'scheduler.tests.test_job'
+        job.interval = 30
+        job.interval_unit = 'seconds'
+        with self.assertRaises(ValidationError):
+            job.clean_interval_unit()
+
+    def test_clean_not_multiple(self):
+        job = self.JobClass()
+        job.queue = list(settings.RQ_QUEUES)[0]
+        job.callable = 'scheduler.tests.test_job'
+        job.interval = 121
+        job.interval_unit = 'seconds'
+        with self.assertRaises(ValidationError):
+            job.clean_interval_unit()
+
     def test_interval_seconds_weeks(self):
         job = RepeatableJob()
         job.interval = 2