I don't smoke before work personally, but if it really helps you with your job then do it. However, appearance is important to customers and therefore important to your managers, and directors. If you appear stoned and the customers are noticing then it's probs not a good idea, unless you can shrug it off onto some other legit reason. But the fact your manager knows you smoke makes the whole thing a bit iffy. People seem to be too trusting at times (especially in the work enviroment), so regardless of how understanding your manager may appear the possibility is there that it's being used as ammunition. Like I say if you feel you can pull of being stoned at work, and have a valid reason for doing so then go for it. Just be very careful, and maybe think twice as to whether or not you really need that joint.