Budgeting options include Daily, Weekly or Open at the Ad Set level. Budgets run from 8AM EST current day and resets at 8AM EST the following day.
Daily: designated daily amount
Weekly: allocate same or unique budget per day of the week; Allotting $0 to a day(s) will pause your campaign/ad set for that day
Open: uncapped spending until funds are depleted for a given campaign/ad set