how did you find out? 🙂 RTC time and timecode are displayed on different pages. You cannot see them both at the same time on your iPhone.
Anyway, I did a test here. RTC and timecode did match up perfectly in sync (you can see them both by using the Mac Setup App). The only thing that can cause a difference between timecode and RTC is when using NTSC timecode with 29.97 fps NDF. Here the timecode runs slower than real time. After one hour the difference between RTC and timecode will be 3.6 seconds.
Hope that helps!