It really depends on the type of game and how it presents itself.
Some games have a very long and complex story but others might have a shorter story told more indirectly, then there are also multi-ending games which might take longer than a regular story game since you have to replay them. Then there are sandbox games which don’t necessarily have a limit on how long they can be since it’s dependent on how much you want to put into them.
Ultimately in my opinion there’s not really a required amount of time for completion, the thing that I think is most important is whether the games are fun and enjoyable. In the case of story games they can be as long or short as needed depending on how they tell a story.