This is a really great game! The concept is really unique and it's very original for the theme. The game is also very polished and it looks great. I especially like the way you did the menu. It's very cool and it also immediately introduces the player to the movement mechanics. And the extra additions once you complete the levels are also a really nice touch.
The music is a tiny bit repetitive, but I really appreciate the effort of every level having it's own music and the music changing once you steal the gem.
The items might need a little bit of work. The clock is (like you mentioned) a bit underpowered compared to the rest. The items are also never really necessary, since they spawn randomly. Maybe if they had fixed spawns, or if you could pick and bring one or two of them with you into the level, it would allow for more planning and strategic play.
I also got stuck in the slime for a really long time, a couple of times. It feels like the time is a bit random. Maybe you could make getting (un)stuck more explicit by adding some sound effects?
I really like this game, well done!
I'd really appreciate it if you would have a look at my game as well, and be sure to download the smaller version :D