Do not depend on the destination
Resort-area stations may have limited or seasonal hours. Fuel in the city while you have several alternatives.
Longer routes need a larger margin
Shiga Kogen and Myoko require more time and elevation than nearby Togari or Nozawa. Snow, queues and road restrictions can increase fuel use.
Work backwards from the rental return
If your contract requires a full tank, allow time to leave the resort, find an open station, keep the receipt and complete the return inspection.