Not much time . . .
Risk of getting oral cancer
from chewing/dipping tobacco depends upon how much you chew/dip and how frequently you do so.
It also depends upon placement (same every time or different each time) as well as intangibles like family genetics. Best to think in terms of years. Better than trying to calculate your risk, just quit chewing/dipping. Living w/your tongue and/or jaw removed isn't fun.