My upgrade is on April 19th at 10am, so they're starting to go out. I've always found that logging into your ticket manager and clicking "upgrade seats" on the left side, gives you more of a heads up on your date/time than waiting for a call or email.
Got my seats today, number 1250ish on the list. Had a lot of options to pick from, so they're still working down that list! Ended up with 309, dead center on the 50.