So I was gone from this speedrunning community for a while and I came back today only to find out that you need to submit the RTA. Can someone help me out cause I don't know how to record the length of each run in real time.

You can open up your recorded run in any video player you like, and open up a timer such as Livesplit. You can even just mark the times in the video player. The rules determine when your run starts and ends depending on the category you're running, so follow those rules, and submit the time. The timer is not required to be on screen.

thank you

In IL runs start the timer on the input that starts the mission, on Battle for Hyrule Field that's the A press that ends the load screen, on most other stages it's the + that skips the cutscene. We're trying to time gameplay not loading.

On some levels (Calamity Strikes and others) there's a load that's counted towards your time because it happens right after the input that starts the level (cutscene skip) - If you watch some of the cutscene it'll reduce that load so make sure you do that if you don't want that load screen counted in your time.