The bottom line answer to the question is, " When you want to." 
However I believe that it is said that if you pass the pencil test then you ought to wear a bra full time. Before anyone asks, the pencil test is whether an ordinary pencil will stay put in the crease underneath your breasts when you are standing upright ( and no, I don't pass the test and don't wear one full time).
However I believe that it is said that if you pass the pencil test then you ought to wear a bra full time. Before anyone asks, the pencil test is whether an ordinary pencil will stay put in the crease underneath your breasts when you are standing upright ( and no, I don't pass the test and don't wear one full time).