I want to make a run but I can't play at once. Is it OK to make parts/episodes? What are the rules of that? If it has to be in one piece? Would it be OK to open a steam on Twitch and pause the game for a while and continue?

As I see, this guy (https://www.speedrun.com/gtavc/run/m7gvnn5m) made a 25h run and video is 76 minutes. I believe it has other parts.

no
has to be in one piece

The run has to be in one sitting. If you pause to sleep etc, that will be added to your time. We need evidence that nothing has happened inbetween sessions.

That video you linked is via a website that doesn't embed things properly. At the time of the submission, the full video existed.

@bekir911bekir911 Pausing is allowed, but it doesn't mean that stops the timer, since the runs are timed in RTA. Twitch has a 48 hour stream length limit, so you're free to do so.

Thanks for your replies. I believe it's OK to record as a video and upload to YouTube, right? And do I need to add a timer or is video timer enough?

YouTube is fine, and a timer isn't required.