yup, mine turns on after about 40 mins of driving. its almost spot on too.... like approx 40-45 mins on the freeway, and bam, it turns on

 

how much does the tire pressure need to drop for the light to come on..my has been on 2 days now, i haven't had time to track down a gauge and check them, but none of the tires look lower, and the car isn't handling any different. as stated above the temp here has dropped pretty low the past couple days, but i can't see that making a big drop in psi. any advice other than bringing it to the dealer?

 

It doesn't take much - you'd be surprised. If you're borderline on your air and the temp drops pretty low it'll come on - it'll usually go off once the tires warm up - mine has in the past. I was about a pound below the 'trigger' but it was in the 20s outside. After a few miles on the interstate it went off, but the tire was low.

My experience has been that it lights around 28 PSI or so, +/-.. I had a slow leak a while back and it took me a few days to get it fixed. Rather than pull the spare, I just added a little air, it was only losing a pound every couple of days.

Grab a gauge and check it. I was at 25 PSI before I got one on mine and except for the light I didn't feel jack. Mine was the right rear.

 

+1.^^ Just went through it myself..

 

I had the same thing happen on the highway using winters - it eventually comes on.
However, it came on when I had my OEM Michelin's. I checked the pressure - sure enough it was right, the tire was down to 25 PSI. I repressurized to 35 PSI but the light came on again next day. Brought it in and it turns out I had a nail in the tire so it definitely works.

 

We had the same thing happen when the temp drop. Pulled out the compressor and air them up to 32psi and it was good to go.