That'll depend on the quality of road you're travelling, the kind of bus it is[if it stops at every other km to take on/off passengers, you might be screwed]. Oh and some bus drivers love to randomly stop at dhabas for half an hours for totally useless reasons. Factor that in the travel plans as well. Honestly, unless and until someone has gone on that route before[and more specifically, on that specific road since multiple bus routes exist], it's hard to get an exact answer. That being said, one thing being in your favor is that you beat the early morning rush by starting at a good time.