The first answer is generally correct, it is the second conditional form.
The reason why it was used here:
The first conditional "If I don't get up early, I will miss the bus." is used when the "if" statement is either in the future or a general rule. ("If you jump into the river, you will get wet.")
In your example, the second conditional is used because it describes a decision (getting over-time) that has already been made and it is already a fact.
You would use the first conditional here if either no extra hours were made until now or if it is uncertain if you get over-time.