I got the exact same thing from ACR, only they said that I had 7 days to use it or they would take it back. I tried a $25 GTD for 50 cents and won around a buck, but I didn't have the time to keep grinding these for a week so I just put the whole wad in on a $5.50 MTT.
Min-cashed for ~$9.75 and the money's still in my roll there, so I guess with 6 cents or whatever was left after I bought in that qualified me to keep it. Wow do people play crazy in these re-buys, it's just nothing but bingo all the way to the FT.
If there was no time limit I would have used it to buy into the cheapest tourneys possible and tried to grind up a roll from there, or used it to get a little experience at the lowest cash stakes since I have virtually none.