Like mentioned in the title, I'm not sure if I can record a speedrun (which belongs to the longer speedruns (like 1h+)) because of irl stuff and limited time. So would it be allowed to do that?

The vast majority of leaderboards require runs to be done in a single segment. Some games have exceptions but those are usually only for extremely long categories (like, 24+ hours). Check with the moderators/community of the specific game you're wanting to run, but most likely you won't be able to.