it really depends on what you look like prior to the HT. IF you are used to buzzing your hair to a #2/#3 guard, then you can go back to work after a few weeks and no one would notice you did anything since you hair will be the same length.
However, if you wore your hair long (a few inches), then it'll look awkward when you come back since you have to shave the recipient area. Ie. if you needed a few thousand grafts, the shave would be noticeable since there will be a bald patch where the shaving was done.
If you want NO ONE to notice, then just remember hair grows 1/2 inch/month, so you can calculate how much time you need.