Depends entirely on tank size really.
Standard (in Australia) is 2x45kg household cylinders (chest high to an adult) for household cooking.
(Finish one, switch to the other while waiting for swap).
It's not hard to have eight or more cyclinders on standby and to keep them topped up for when needed.
For rural / quasi industrial, furnaces, generators, etc it's not uncommon to have fixed installation 210kg LPG bulk cylinders filled by supply truck .. and larger.
When disaster strikes a bulk tank lasts a long time if the primary drains on it (eg: a tile or glass furnace) are wound back or turned off.
Eg: https://www.supagas.com.au/for-home/lpg-gas-bottles/tanks