Livesplit is a tool that lets you make a splits for any game. You'll want to have at least 8 splits so you have one for each level. Although 1 more might be desirable as you might want to know when you enter the banshee fight.

Many thanks to SuicideMachine for the load remover and auto splitter they made.

(To make the run easy to start you'll want to set global hotkeys and deactive for other programs under settings)