The only way for the game to run at a normal speed and with normal load times i need to play it in fullscreen, because of this i cant use a timer like LiveSplit, so can i just use the video length as a time-frame?

I can't speak for the other mods, but if you would like to submit a run without a timer, I'd be willing to time it for you when accepting the run. I would not use video length, opting for timing it myself from start of movement to whatever the given ending's end is (usually with a black screen or end of movement).

cutting the video to find the time is good enough in my book

I like ZZKer's answer better