I would think You would be better off installing an aftermarket hour meter or looking at your watch and just keeping track, hours per tank is going to greatly depend on how you ride and is not going to be very accurate.
I generally just open the good ole gas cap! I know that I ride my bike like a maniac and I can ride all day on the same tank of fuel. When it looks a little thin, I go to reserve and head for the trailer. I haven't been stranded yet. It's also a good idea to ride with others in the vent that you run dry!