in my shipping experience, as long as it's sent out a day or so after the auction ends it should get there in time for you, but that's just my opinion :) I've had some packages I received that took almost three weeks to get here, but that's worst case scenario, and that was from shipping date to here, not winning to here.....but I'd say if you win you should be ok!
To add a picture after a bid has been placed, try contacting Listia here: http://help.listia.com/requests/new You can attach the pictures you'd like them to add that the bottom of the form. Be sure to include this auction link as well.