As i write above in october, ButtonMapper had in settings switch to 10minutes timeout,
but now if i look to settings, is here also timeout Never options (in More Options/Flashlight timeout) 
Not know if changes is from ButtonMapper november update, or if depend on some changes in FP5 OTA update, anyway i try FP5 with flashlight on about 1 hour (with lcd off, phone in pocket) and working, phone is only a little warm, i forgot look at exact battery state before, but i think flashlight on for 1hour eat 10% of battery…
BTW: I don’t understand how it can be a phone deal breaker if emergency flashlight have 4minutes timeout… If for someone is important flashlight, then exist much more usable solutions…
I have always in pants pockets Fenix HM51R Ruby V2.0 (is limited/modded (for Czech? EU?) version of Fenix HM50R V2.0) and as backup little/keychain Fenix E03R V2.0