Maybe slightly longer, as it would be easy for someone to just play on the server for 3 days and then grief everyone on the tekkit server once they were allowed. Maybe 1 week would be a decent amount of time for the person to get to be friends with the community and you could make it so for that 1 week they have to play on the server they also have to log into the mumble server or that time doesn't count. But also remember I was griefed by Karclan who has been a member for quite a while, Helljack was the person who checked the logs and banned him so he should know about this aswell.