Been without power 19 days Floyd, 17 with Isabel, and many other times due to Northeaster's...
I averaged 12 hours a day use, mornings and evenings...
Splash lubricated change at 24 hours Dino, 36 semi-synthetic, and 48 for full synthetic..
2, 3, or 4 days...
Water or oil cooled, semi-synthetic, 5 days, 60 hours, full synthetic, 100 hours, 1 week.
I use a sandwich adapter and add an oil cooler...
Fram 3600 or Purolator 20195 filter or equivalent (usually an AutoZone S3600), changed every 100 - 120 hours, 1 week to 10 days...
Boutique oils too expensive, what ever 10W-30 I can get for cheap...
Current is Shell Rotella T5 semi-synthetic, got 10 gallons for free (AutoZone clearance)