A basic loop-de-loop free motion quilt that is baby or throw size 1 to 1.5 hours. This would double for a twin size. But if I want to do some more complicated free motion I plan on more time. This is often difficulty to calculate because I was told the when you get tired, aching shoulders STOP and take a break. I do and I do "resent" my work that way and I don't physically from the work of this beautiful step in the process. I find quilting channels takes me longer and is more tedious for me. I still use the channels but not as much as I see from others. That is only a matter of preference.
I know that planning is a wonderful thing but taking your time and enjoying the process is also part of the joy of quilting. Smile, drop those shoulders and sit up straight, listen to music or a good book on CD and enjoy, enjoy, enjoy.