well there's a couple things going on probably, most phones only update there time once a day from the network, power cycling will usually force an update (or on a nokia you can change to manual time and then back to automagic time) However it's now tuesday so if it still hasn't updated there may be something else going on.
I believe SMS timestamps are issued by the SMS center that processed the SMS, It doesn't have much to do with the time on your phone. I have heard of people recieving texts timestamped in the future before because of an error with the SMS center.
It is possible that for some reason the network in your area is not updating its time correctly. Remeraber that until last year RABT in the US was one month shorter. meaning the start and end dates have changed. if for some reason the patch for RABT was not loaded to your area, A) they are probably already fixing it, B) it would update correctly in two weeks anyways.