This PMCIndia PMPML Time Table should help you.
However, there is criticism about the last timetable being published in 1998.
I think there is a specific silent time during the night when all bus services stop.

ugal Rathi, president of the PMP Pravasi Manch (PMPPM), a city-based organisation working towards the betterment of services offered to PMPML commuters, said, “We have been following up this issue for last four years. On April 13, 2008, they had published 10,000 copies of the timetable for Katraj depot. The copies were to be launched by Ajit Pawar but it didn’t happen due to last-minute change of his plans. We feel they do not want to publish timetable because then there will be an obligation to abide by it.”

I think, calling up the depot with this question (or someone who can walk over to one of these places) would be able to give a much better answer. There is also contact info at that site.