I understand that it’s important to have a consistent schedule, but it’s hard to determine when I can consistently commit to the work. I plan to start recording voice overs, and the pressure is mounting to get going soon. The most consistent commitment I can offer would be Saturdays from 1:00 to 3:00 pm, and possibly Monday nights from 8 or 9:00 pm to 10:00 pm. Is it ok to start out at once or twice a week?
Suggest you read the Terms of Service at the bottom of the Fiverr main page for the rules as to how Fiverr works.
Everything is explained there in great detail.
After reading this you will be in a position to make an informed choice as to whether or not this is suitable for you.