I grew annoyed with having to start cheat engine and attach it to Underrail every time, and it spiraled out into a fully-fledged speedhack trainer.
I tried to make it as user-friendly and foolproof as possible. The speeds are bound to F1 up to F4, from normal speed, to double speed, quintuple speed, and x255 speed. You'll need to unbind them in-game before using them (by default F1 is help and F3? hides the hud.)
Personally I use double speed for normal gameplay, quintuple for travel/fishing/skipping things and x255 when I need to pass time, but that's just me.
I'm also attaching the Cheat Engine table in case you want to change the hotkeys or just want to re-make the exe on your own because you don't trust strangers on the internet (it's fine, I'm not offended. What, this? No, I was just cutting some onions.)
Note that if you use the table to re-make the trainer, you should use File -> Generate generic trainer (as opposed to File -> Save as.)
Hopefully this will be as useful to others as it has been to me.
Mega linkMediafire link(I've only tested this on the GOG version of the game, not the Steam one - but it should work regardless.)