Wait period between sessions

I have asked this question before without result so thought I'd re-ask with additional clarification. I have a user group that is only allowed 3hr session times (easily resolved with sql counter module) with a 15 minute wait period between sessions. Has anyone written a module or know of a way to implement this wait period. I was thinking something similar to a module based around the sql max session module only query the sql backend for the last time connected and if the period is less than set variable (15 mins in my case) then reject access with an error message like "Wait Period Enforced" Regards Cory Robson