Commercial terms
Overtime
Definition
Overtime is time worked beyond the booked shift, billed at the hourly rate for the hours actually worked.
In practice
At weddings and evening events the programme almost always slips, so overtime is the rule rather than the exception. It's worth booking a longer shift than planned, so nobody has to decide live. Put the basis of billing in writing in advance: it's the single most common subject of after-the-fact disputes.