The Olympic site has today confirmed that the torch will be leaving Southgate College at 3.58.
As previously reported, it will then be heading past Southgate underground station before turning down The Bourne and into Palmers Green. So we should be seeing it a little while after 4.
If you cant quite make it in person, you can see the relay live at http://www.london2012.com/torch-relay/video/live.html