HonestlyIn almost 20 years of business experience, I never encountered the use of before time
before time in this context - and I have business experience for almost 20 years. One better alternative is in advance
in advance.
In your example, the task is finished in advance
finished in advance. If you deliver the results on the same day, then you deliver in advance
deliver in advance, but if you deliver the results at the agreed date, then you deliver on time
deliver on time.
The additional point I want to underline is that finish work
finish work and deliver
deliver mean different things.
Alternatives to in advance
in advance: before the deadline
before the deadline, early
early.
Regarding before time
before time, I think it is better suited to poems and legends.
More: in time
in time and on time
on time are both correct.
in time
means "before the deadline"
on time
means (almost) exactly according to deadline
in time means "before the deadline"
on time means (almost) exactly according to deadline