Easy to calculate! put a 1:1 pully on the timer and another pin mark the string (or what ever you have going around maby even a lakky band) let it run for 5 minutes then you can find out how quick its turning then its just a matter of ratios.

youll have a fully self contained dob running on its own . who cares if theres only a 3 hr running time. it takes 2 seconds to get it going again
if i remember a lecture from one of my communications classes for engineering.
"Creativity is not just an idea that is made, it is not a single person, creativity stems from many people often over many meetings to form a single idea/vision that is of the best possible solution"
All hale the amature astronomy community!

w00t