How much time do I have to listen to the mix during each revision
Each revision includes a comfortable five working days time slot, which is a huge advantage of the online mixing service.
Instead of having to make quick decisions while in the studio, you have ample time to check the mix in all your trusted places (personal studio, car, headphones, etc.).
A great mix is not the one that sounds perfect in the expensive studio monitors, but one that sounds awesome in a variety of playback systems.