There is a new scheduling preference option you (or your users) can set on their profile pages. Switch to the assignments tab, and at the top of the Teams sections, you'll see the new option.
The times per month option was already there, but it is now joined by a new times per day option. The word times in this case means 'plans', but since your users probably don't know what a plan is, we used a simpler word.
If I say I only want to be scheduled 1 time (plan) per day, if I'm scheduled to a Sunday Morning Service, if someone tries to schedule me for a Sunday Night Service (a different plan), it will show a scheduling preference conflict.
It is important to note that the word 'times' can potentially also be confusing. In this case it does not refer to multiple times within the same plan. So if I am scheduled to Ushers 9am and you try to add me to Ushers 10:30am in the same plan, you will not receive a conflict warning. Since they are both in the same plan, it doesn't trigger the preference conflict.