Platinum, Ultimate and Awesome Time Determination

As you probably know, determining the Platinum Time and the Ultimate Time is a primordial step in level building, but can take several hours to be done correctly. Besides, there is the invention of the Awesome Time which, I remind it, is supposed to be the super-hard time to beat.
And hard to beat sometimes means hard for the level builder to determine!
So, my question is: do you guys know some useful tips to help determining PT/UT/AT, so, depending on the level's difficulty, the player doesn't feel like the UT or the AT is way to easy to beat or near-impossible to figure out?

Here's (generally) how we determined these in PQ:

These directions assume you are a competent but not excellent marble blast player. If you are excellent, play very casually for PT/UT and only play seriously for AT. If you are not very competent, get someone else to test for these because it can be very difficult to know how fast your level can go without good play testing.

- Platinum Time is roughly what you get the first time you finish, maybe a little faster. Should be trivial for you to beat because (we're assuming) you're competent. It will be harder for newer players because they are less competent. In PQ we aimed for roughly 75% of people to beat these (Number might be off. Matan, correct me if you see this)
- Ultimate Time is roughly what you get on a decent run, should be reasonably difficult for you to beat, I'd say maybe 25% of the time. This will be more challenging for new players and somewhat challenging for excellent players. We expected about 30% of people to beat these.
- Awesome Time you probably want to ask an excellent player to find for you. Get their best possible time and round to the nearest 0.5 second or so (for medium sized levels at least). Often these involve finding weird paths that you, as the level designer, didn't intend. That makes them very difficult to set unless you get someone else to test for you. If you have to test it yourself, try doing a "fastest of all segments" run where you sum your fastest time to beat each challenge. Then probably subtract 10% because people are very good at finding faster paths. Generally you probably won't be able to beat this time, and anyone who is excellent will have considerable difficulty. In PQ we used the best time from all devs and four testers to set the ATs. We expected 5% or less of people to beat these, and set them pretty much as low as we thought was possible.