modified Monthly Quota

Dear All, I want to define a plan on free radius like this: User has maximum of 10GB of traffic per month. Between 1am and 8am the traffic is free so not counted against that 10GB. Accounting interims are setup for every 5 minutes. I'm using freeradius 1.1.6<->Mysql Any suggestions for implementing this? Any ideas? Thank you in advance, Parham