Yeah, a timer could be a nice addition (I was also thinking about adding a death counter, but didn't have enough time to do so).
The hammers in level 5 should be perfectly visible once you were squashed by them, so I guess you're referring to the projectiles in the level 7 and 9 (the last one). Maybe it was conveyed too poorly, but having to rely on the sound was my intention here :)
Thanks a lot for the feedback! I'm really glad you enjoyed my game :)