Leroux: Dominique Pamplemousse was mentioned before, but it's not in the OP's list yet. Takes 60-90 minutes to complete, and it's probably safer to complete it in one sitting, because while it does automatically save your current progress when you quit, it's made in Flash and I supect that clearing your internet cache also deletes your save game data (happened to me with this game, as well as another Flash based game in the past).

Grargar: Crystal Caves, which is the game that Secret Agent was cloned from, can also be completed in some hours, despite the copious amounts of trial and error included.

Grargar: Even with the DLC, Renegade Ops took me a bit over 4 hours to complete it (even if at some point, I thought that stages were a bit long, there are not of them in the game).

fishbaits: Spelunky is one that I`d suggest for this list.
From what I recall, it`s half an hour plus if you take it steady from start to end.

madth3: I played Morphopolis last night and finished it in an hour and half.

You are looking for hidden objects but with slightly different mechanics than usual HOGs. Recommended if you can get it for a cheap price.

madth3: At less than 3 hours, I suppose The Room is another candidate for the list.

IAmSinistar: Thanks, I've put it on the list. It's one I've wanted to play, but they'll have to release it DRM-free first.

madth3: I guess the Android version has less spectacular assets but it's cheap. You can also get part two there.

IAmSinistar: Probably the only downside is that the game isn't based off the classic movie. ;)