I had something similar happen yesterday. The Date had move forward by 1 day but the time was 15 minutes behind. If I turned off "Set Automatically" in "GENERAL - DATE & TIME", it would keep correct time. The only problem with this is I have found most mobile phones tend to drift in time accuracy and have always synced the time to the carrier to prevent this.
If I set the time manually then enable Set Automatically again, the date and time go back to 1 day forward and 15 minutes back again. I trawled through the forums and found HEAPS of other people with the same problem.
Some of the solutions seemed a bit severe (completely wiping and restoring the iPhone) so I tried the following and it worked for me:
- set time & date manually by turning off "Set Automatically" in "GENERAL - DATE & TIME"
- ensure date, time & region setting are correct on both your computer and iPhone
- connect to iTunes and sync
- after sync has completed, turn on "Set Automatically"
Some people have said that this didn't work for them, but so far, so good for me.
I've noticed a few people saying on the forums that you should just forget using the Set Automatically option because of this issue, but really, if Apple are really serious about making their product the best, easiest to use on the market, they really should fix problems like this that are affecting "grass roots" features like carrier time syncing. I've had Nokia GSM phones for years and have never had this issue with them.