Bethesda head of publishing Pete Hines shared his experience playing Starfield. He has spent nearly 200 hours in the game, but is still far from finishing it.
Pete Hines stated: “There is not an amount of time where I’d say, ‘Now you’ve played enough Starfield to get what this game is.’ I’m at 150, 160 hours on my current playthrough, and I haven’t even come close [to finishing].” There is still a lot he deliberately hasn't touched.
Starfield's main quest can be completed in 30–40 hours, but there are also various side activities in which one can get bogged down for a long time.