The best time to change the time is at the start of a new pack. If you're going to go to work around the same time each day, maybe you could continue taking it at 3:45 for the rest of this pack. You should be fine, though, so long as you're not missing pills and you either continue this 3:45 time or your normal 7:30 time from here on out. While it is possible to get pregnant, it's a small percentage of a chance at this point.
Yes you can get pregnant, no contraception on its own is100% safe, but I would say only if you're extremely unlucky that you would fall pregnant this way.
I suggest that you stop worrying. If things don't feel right with you in 3-4 weeks time take a pregnancy test or go to your GP for a free test.
Good luck!