Lucky enough, the last 2 dragon balls they gave out yesterday I was missing and didn't have to forget about it. I'm almost positive if you get them, you can accept them within a certain amount of time. I've been sent a lot of items and accepted them 2, 3 maybe 4 days later. I only need to make 2 more wishes (1 new ultimate attack [Minus Energy Ball] and Power Pole) and I have nearly everything in the game except for Z souls. After that, I won't need to hunt for dragon balls anymore and i'll leave them in there to see if they stay and i'll post it here in the future.