Now, just to update, I tried to do the time zone thing last night, and it worked! I was able to give three different cars to TrackStarGT/RayderRN within about twenty minutes! Here's what I think happened:
When I tested it yesterday, it was about 2:30pm EST (my time) on Dec. 3, and I moved the time zone as far forward as possible, to GMT+11hrs I think, so that the PS3 thought it was about 7:30am Dec. 4, and it did NOT reset my gift car limit. I couldn't give a car. But then last night, again at around 11:20pm (Dec. 3), I moved the time zone ahead by only one hour, so that the PS3 thought it was 12:20am Dec. 4, and it worked, I gifted a car to TrackStarGT/RayderRN. So I thought, well, it must know somehow that the big jump from GMT-5hrs (EST) to GMT+11hrs was not legit, but when I only jumped ahead by one hour, it couldn't distinguish. I jumped ahead one hour to a time zone that was still within Canada (my country), so I think maybe the game or the system tries to match your time zone with the country you said you're from when you first create the account. If they don't match (if you said you're in Canada but you change the time zone to a Russian time zone) the game won't reset your gift car limit, but if they do match (if you said you're in Canada and you change the time zone to another Canadian time zone) then it WILL reset you gift car limit, and you will be able to give another car.
That's not the best part. This means that you can still only give two cars every two days, for even though you give two in one day, the game THINKS it's the next day, so you still can't give any more cars until the next day (in this case, I can give two cars on Dec. 3 by lying to the game and saying the second one is actually given on Dec. 4, but I still can't give another gift car until 12:01am Dec. 5). So you couldn't give two cars per day, you can just trick the game into letting you give two cars one at the price of zero cars the next day. That is the cost. It would allow quicker two-for-ones, but not MORE trades.
BUT I was able to give TrackStarGT/RayderRN three cars in twenty minutes, as well as the one the previous night, after midnight, for a total of four cars in one twenty-four hour period. I did this by the following procedure, see if you can figure out what the system is doing to allow this, maybe we can exploit it for unlimited gift cars until they finally remove the limit in a patch (I hope):
1. Gifted a car at 12:30am Dec. 3. In theory, I can no longer gift another car until 12:01am Dec. 4
2. At 11:20-ish pm Dec. 3, I tried to gift a car, and the game would not let me
3. I quit the game, set the time zone one hour forward so that at 11:20pm EST Dec. 3 the game thought it was 12:20am Dec. 4, and then I restarted the game.
4. When the game loaded, I was given five new museum cards, and when I tried to gift a car, it worked. I then wanted to test if I could re-reset it.
5. I quit the game, set the time zone BACK to EST (it was about 11:30pm Dec. 3)
6. I restarted the game, tried to gift a car, and it didn't work. However at this point I believe the game reset the next day's limit because:
7. I quit the game, set the time zone forward so that it was 12:30-ish am Dec. 4,
8. Restarted the game, tried to gift a car, and it worked! That's 3 cars since 12:30am Dec. 3, at about 11:30pm Dec. 3, the same day.
9. When I quit and did it again (time zone back one hour, restart, quit, time zone forward one hour, restart, gift) the same as above, it didn't work
10. So I tried moving the time zone back further, but still within the same country, and then forward again, and it worked. I was able to gift ANOTHER car, for a total of four cars in one twenty-four hour period, and three in twenty minutes or so.
Tonight I will take notes and give more details tomorrow, so we can maybe find the upper limit here, but I think it has to do with the number of time zones in your country. If anyone else has any thoughts here, please chime in. I will also try to get TrackStarGT/RayderRN to chime in here to confirm that he did indeed get three cars from me in twenty minutes (how are you doing that? he said, ha-ha) and four in twenty-four hours.