Thanks for the feedback! I provided my thoughts on the skip turn mechanic in my response to Weakest Imp.
I'm glad that you liked my puzzles! I essentially came up with "mechanics", like the clock power up, enemies, the keys, boxes, etc. Then tried to make a level that only uses one of those mechanics in a relatively fail free environment to introduce/teach it. Then I'd mix and match the mechanics to have them interact (enemies on moving platforms, boxes to block enemies, etc).
As in designing the levels, I essentially made a start and end position and played around with moving to it. I then would look to see where I could roadblock the player with the mechanics (an enemy here, or a detour to a key). I felt putting restrictions on myself made it easier, especially keeping everything to one screen.
Making the levels was definitely the most time consuming part, with ideas just "popping" in my head while I was doing other things. I definitely wanted to make more levels, but due to time I just tried to polish what I had. Was going to have more enemy types and a boss as well.