Gifts for visiting other cities.

OK, I have been running a check on when the mayor gift bubbles are reset and it appears to be at 4 hour intervals based on USA Pacific Standard Time (GMT -8), which is likely the EA office this game is run out of.

I have seen bubbles in most cities at midnight, 4am, 8am, noon, 4pm, and 8pm Pacific Time. A lot of bubbles are still there an hour later but are nearly gone 2 hours later. This had nothing to do with buying anything, which I didn't, or any other variable, just time. Remember, this is Pacific time (GMT -8). That is important. Hope this helps.