Can you base a film review without watching the whole film?

[dojj singh]

This isn't so much of a carry over from the "Walked out of a movie" (because some of them were right) but more along the lines of how much of a film do you need to see before you are confident you can stay/leave/switch channels.

I'm currently 30 minutes into the remake of Get Carter and haven't found it to be as terrible as everyone else has made out.

Of course, I may post back in 5 minutes and say that I was totally wrong lol.

But generally, how much of a film do you have to suffer before it dawns on you that your time would have been better spent watch paint dry?