Hi
If the builders finished the work to schedule, they would receive a bonus.
--- Shouldn't it rather be: "... they would have received a bonus"?
There are a few ways to say this depending on the meaning.
The second way is only possible if you amend the 'if' clause.
1. An habitual action in the past.
We had this arrangement. If the builders finished on schedule, they would receive a bonus. (Your first sentence).
2. After work completion, you, the boss, say to the foreman:
If the workers had finished on schedule, they would have received a bonus.
I can't think of an application for "If the builders finished the work to schedule, they would have received a bonus". If
you can, what is the context?