Good game, with original enough gameplay. I like to think of them as the "Present" (regular guy), "Past" or "Mystical" (robed guy), and "Future" (science guy). Nice details and fun little game.
There was one problem I confirmed though, and not unique to this game (although it is a game design flaw because it can be corrected on the developer's end). When you make games that have timing-based requirements or achievements, you should never base that on system clock speed, which is exactly what you based it on. In short, those with worse hardware have an unfair disadvantage and those with better hardware, an unfair advantage. If you're having problems obtaining the timing-based medals, lower the quality and see what I mean -- huge drops in level complete times!
With the quality on low, and with much effort I was barely able to squeeze 19:00 on the dot which thankfully awarded that last medal. With a better computer, lower times could easier be achieved. With a worse computer, perhaps at some point it's not even possible.
Either do one of two things with timing
1) Base it on frames rather than system time. This is probably the easiest fix.
2) Adjust accordingly. Start an internal timer, stress the system, stop the timer, compare the time with that expected and, if it's greater, use this as your adjustment to subtract from player time. Not perfect, because greater stress leads to increased time discrepancies and perhaps you adjust too little or too much, but better than relying on raw system clock speed.
Whatever you do, never base timing on system time. Common game programming mistake.