You're probably OK if you have been clean since 4/20 - drink lots of water, its really the only thing that works.
As for hitting it on the weekends, not unless you are a really skinny fucker with a super fast metabolism - risking your job for a toke seems a bit much.
Me, I smoke every night - There's something to be said for not having to worry about that anymore.
Good luck my friend.
GWN