How many casts before changing it up????

if i have been to a spot on lake that i have caught fish before   will hit it with about 12 cast and change baits. and will go both ways  maybe 20 ft from bank next time 30 ft from bank   back and forth.   place i never fished before  i will give it a little more time maybe 25 cast each bait and be sure to go back over same place have caught a lot of bass the second time  i guess just coming from a different angle   kb