Any hours that you work above 40 hours in a pay period, will be calculated at an overtime rate. However, the shift that counts towards overtime is based on which shift was last confirmed in that pay period.
For example: A nurse gets confirmed for shifts on Sunday, Monday, Wednesday, Thursday, and Saturday in a single pay period. These would all be regular hours worked. However, the nurse then gets confirmed for a shift on Tuesday during the same pay period. Since this shift was the last to be confirmed, this is the shift that would count towards overtime.
Also note, since overtime is calculated by confirmed shifts, when a shift is not properly cancelled or called out of through the ESHYFT app it does still count toward overall hours for the work week.