I charge all mine at 2C and dont seem to have any problems. You should be able to get to 80% charge in 20 minutes at 2C. As long as you are fully charged before your first heat then you shouldnt have a problem running a single pack with only 20min between rounds. You wont get to practice between rounds though.
I believe ROAR only allows 1C charging though for safety. So make sure you are following the rules wherever you race.