Weekends? No way is that not peak hours. You'd also have the problem of if you offered free data on nights and weekends some people who only have smart phones and no computers (it exists) would just switch over to their mobile data plan instead of a wired house data connection. This would effectively switch everyone over to their network during peak data usage hours. That would be an incredibly bad idea.
Perhaps. But free nights and weekends would still be better than a shared data plan. :-\