Ive only been able to race 13 times this year (frequent bad weather) and am just finishing my 5th gallon. Admittedly I dont practice much at all or use a lot of fuel breaking in new engines but I do finish 95% of all my races and run many long mains.
Between races I spend on average probably 5-6 hours cleaning and preparing but if I cut the TV off I am certain I could cut that down to 2-3 hours. Mostly I just clean and check over. I do diffs or shocks around every gallon of fuel or so but mainly base that on the importance of the race I will be attending or if I expect track conditions I may not be setup for. I regularly replace clutch bearings and air filters between races but have been known to occassionally push them multiple races if they look good enough.