IPhone :: Received Advanced Replacement IP 4 / Clock Is Out Of Sync?

I called applecare this week because of a number of issues with my iPhone 4 (got on launch day). The advanced replacement came today so I have two for a short period. First thing I noticed was that the new phone (SN: 85028...) has a MUCH warmer screen than the original (SN: 86022...). At maximum brightness the new one looks better and a tad bit brighter but at 60% or so (where I usually use it), the original wins as the new one looks filthy). I'm not sure that I like it and think I want to keep my original but am still concerned about the other issues:

-No change in abrupt signal drop when touching the bottom left corner.If anything the signal drops faster with the new phone

-The other issue was that my original iPhone 4 was outrageously unstable.It would crash over and over despite me restoring it, etcIt would lock up after sync, etc as well.One thing I did notice was that the clock is off by 31 seconds.I actually did notice this when compared to my 3gs when I first got it but then forgot about it.3GS and new iPhone 4 = exactly the same clock time old iPhone 4 (from launch) = 31 seconds slower than the others.I find this very odd. Does anyone know what might cause this? I am wondering if something is corrupt in the phone. Also, if I decide that I am truly unhappy with the screen on the replacement, can I just send it back instead of sending my original back?