Great question! It varies on the actual bacteria involved, and the environment they’re trying to live in. In optimal conditions, a bacterium can divide into two daughter cells in 10-20 minutes – meaning that after an hour you could have up 64 cells, and 2^144 bacteria after 24 hours!
However, when conditions aren’t so great, most species of bacteria can survive for weeks or longer by going to a semi-dormant state. Bacillus and Clostridium also have an extra survival technique: spores. A spore is like a seed, containing all the instructions to build the bacteria when conditions improve. These can survive many years before yielding a living bacteria again.
I am not sure if anyone has ever looked to see how long a single bacterium cell lives for. For fast growing cells like E. coli I cannot imagine a single cell lasting more than a few months without it eventually dying or going into a vegetative state but that is just an educate guess.
Mycobacterium tuberculosis is a very slow growing bacteria and can lay dormant in the soil and even in your body for many years because it grows so slowly. One cell takes 24 hours to divide at its fastest rate (compared to E. coli which only takes 20 minutes)