How long is too long?

Honestly, I don't think there's a such thing as 'too long', it all just depends on what you're doing with it.

I've seen films that are over 2 hours long and are fully engaging and you don't even realize how long the film is and I've also seen films that are like 90 minutes long but feel so much longer because of how much of an utter slog they were, y'know?

It's the same thing with long-running franchises as well, like I'm a huge fan of Doctor Who and that show has been on the air since 1963 (albeit with a gap between the end of the original run in 1989 and the series' revival in 2005, with a TV movie in 1996 in the middle of that) and is going to premiere its 40th season in May and yet I don't think the series has gone on for too long. But there's also other series I've seen that have had much, much shorter runs that still overstayed their welcome.