How many crews per frame are you running?
It very much depends on the customer rotational schedule.
As an ad-hoc operator, we call 'em in as needed.
When they work, they are paid well, when not working, they sit by their pools sipping marguaritas.
Recent flying was a good example.
One augmented crew only needed initially (with two or three day slips at each end, as scheduled), however, extra turns were requested, so another crew was brought in on very short notice.