Cool concept, the art is a bit all over the place, and the parts that are pixely don't use nearest neighbor, so they are blurry. It was not at all clear that you have to hold tab for bullet time to switch your countdown with the countdown of something else. Some sound effects for switching to bullet time and a visual cue that you are in bullet time would also be good. If the time is up, don't just pause the game, but show something, and do something. Is there a narrative reason for the game to end if the timer is over, like an explosive strapped to the main character. If so, then you could lean in to that, and make an according game over screen when that happens.
Visual feedback is always great, e.g. when you switch countdowns with something else, you could have the numbers actually switch places. Of course that's a lot more work, and for a 4-day jam you probably didn't have the time for that level of polish, but for things like that, you could look at something like the unity tweens module.
I don't get how you are supposed to use the bomb at one point, because you need it at the top of a moving platform, but I can't pick up the bomb, and the moving platform doesn't go far enough down for me to roll the bomb onto it.
Cool idea, a lot of room for improvement.