docs(known limitations): rewrite and add heading (#17623)

Co-authored-by: Rhys Arkins <rhys@arkins.net>

docs/usage/known-limitations.md

@@ -21,8 +21,12 @@ For scheduled action to take place, both these need to happen:
 - The bot needs to run against your repository
 - The current time needs to fall within your repository's configured schedule
 
-For the GitHub hosted app, all active repositories will be enqueued hourly by default, but it's often the case that not every repository gets processed every hour.
-For this reason, it's best to allow for a minimum 2-3 hours schedule window per run, if you want a high chance that the bot will have run on your repo at least once while the schedule is active.
+### GitHub hosted app scheduled jobs
+
+On the GitHub hosted app Mend checks each active repository approximately every 3 hours, if no activity has been seen before then (merged PRs, etc).
+
+For this reason, you should set your schedule window to at least three or four hours.
+This makes it likely that Renovate bot checks your repository at least once during the schedule.
 
 ## Automerge limitations