Really, the only time music ever slowed down for me was using a turntable that wasn't quartz locked or the pitch/tempo was altered. For how I listen and experience audio, the music always pretty much keeps its recorded tempo IME.

Actually this is a funny point, but true for me too.  I have had a lot of experiences where time feels like it speeds up or slows down, but I never get that with music.

My experiences are the same as Anax's .. unless I play with the pitch control of course.
Never had that with music, I do get other effects when coming 'in the zone' but can get in 'the zone' with a Sansa Fuze + KSC75 equeally well.

The time slowing down thing I only experienced once.
Riding a moped I crashed into a dog at full speed (jumped out of a shrubbery, did not see it)
Before one asks... the dog was quite big and was O.K. (surprisingly)
Falling to the ground went very fast acc to the dogs owner but seemed to take ages and strangely enough heard my Jiu Jitsu teacher 'coach' me how to break my fall.
You know... one arm in, make an arch... roll ... slam your arm on the mat (was the road here) and roll through and stand up.
This all passed very slowly as if I had lots of time.

The dogs owner was surprised as he saw me smacking to the ground, roll and stand on my feet.
No damage... except the moped.
The dog ran away but later came back to the owner.
After a chat to see if all were allright we went our own way again.

Never experienced time slowing down after that (fortunately)

Music is slower when I'm wide awake and faster when I'm getting tired. Perceptively, of course. You might have just been super hyped for getting to listen to whatever it was you listened to.

Personally, I only ever get the "time slowing down" sensation under extreme stress.

Probably the most vivid experience was once when I was too distracted while I was driving, almost ran a red light, and narrowly avoided an accident after slamming on the brakes.  I actually have this odd memory of time running backwards for some reason.

My most vivid recollection of time dilation didn't involve a car crash, but a girl and a slow song...

...and an Adam's apple.