My main hours of operation are Monday - Friday 8am - 5pm, EST. I check my messages throughout the day, and I am pleased to accommodate the schedules of clients in other time zones.
Payments are divided into milestones. For example, a $2,500 project might be divided into 2 payments. A portion due when the concept has been developed, and the overall model and textures are completed, with the remainder due upon complete delivery.
I like to be specific with deadlines, and deliverables. The clearer the expectations, the better the project experience for both of us.