It may look something like this: Obviously, he is not doing it fast but you understand the idea. At the end of the video he finish in 10:29 as it appears on that window.

Also, at the end of a game, a window appears with a timer "PLAYTIME xx:xx" and it looks good for speedrunning in my opinion.

I'm talking about multiplayer offline by the way

I think it would be a good idea to include a new category based on the multiplayer mode (but only one or two players allowed) as there are a lot of areas for siege (here for example we can choose between spawning with 3 weapons, with one weapon or we can choose to play without weapons) and capture the flag if it's not too boring but only few flags would be fun. Also, we can choose between starting with charge boots or we can just find them in the boxes.