It's not that complicated to get all the endings compared to something like Steins;Gate and the routes themselves aren't that long, at most they're like 2-3 hours if I remember correctly but some are on the shorter side, although there's quite a few endings. You could do them pretty quickly as they don't really change the common route that much, but the process is a little tedious and somewhat time consuming. Depending on how many/which delusions you viewed during the common route though, it could be done much quicker.

I'll give a rough estimate of like 12-14 hours to get all the endings if you're taking your time.