When should you put on your robes?
I'm curious as to who told you wearing robes was beneficial.  There are specific ways of wearing robes (as outlined in the vinaya) that can aid in mindfulness, but the simple act of having them on isn't beneficial on its own.  Be that as it may, I wouldn't put them on until you reached the meditation hall.  Wearing them in public has a bit of a "look at me" quality to it.  Taking the more humble approach is almost always best.  (Cue the folks who are going to say that I'm calling monks immodest or saying they shouldn't wear robes! - there is a distinct difference between lay practitioners and monastics on this subject.)