I know it's in DCA but I forget the time (not long after DCA opens I believe) and place. Apparently it can be hard to find of you don't know where you are going. There was a thread about this a month or two ago. I forget the info however. I'm sure others will be able to answer your questions better than me.
The Disney visa character meet & greet is in the hollywood pictures backlot at DCA.
It's behind the "House of Cards" bar, theres a sign that says Disney visa private
character meet & greet.
It's for 1 1/2 hours daily and starts 1/2 hour after official park opening. Currently that means the Meet & Greet is from 10:30 AM - noon each day. PP has already noted the location.
Whether times and/or location will change with the grand re-opening of DCA on June 15 remains to be seen.