I know that all submitted runs are required to have a timer on it. But LiveSplit seems like kind of a hassle to set up, so can I record without the timer and slap it on in post?

Don't know what game you're playing but most of the games I know don't require livesplit or any sort of timer since and you can retime the run through the vid itself.

If its any game that uses ingame time through a load remover, then livesplit is necessary tho.

I'm new to speedrunning, what's a load remover? also I'm running Ori and the Blind Forest Definitive Edition

Well since you're running Ori, it's highly recommended you setup livesplit since you're able to use the autosplitter/load remover functions.

An autosplitter will automatically read the game's memory and split according to the game.

A load remover will detect loading screens and will automatically pause the timer when loading to keep the runs fair.

In fact, there's a written guide on the game's leaderboard page showing how to setup livesplit for Ori. Here's the guide: https://www.speedrun.com/ori_de/guide/k29yz

thanks