Unless a new time line has come out, they left an hour apart.
Prosecutor General Vladimir Ustinov told Putin he had no clear view of what happened to the planes, which took off from Moscow's Domodedovo airport late on Tuesday around an hour apart for two different destinations. Link to story - 3rd paragraph
approx. 40-45 minutes difference in departure time as you suggest ... less than an hour but more than 10 minutes ... the crashes were close, perhaps they were within 10 minutes?
(maybe that's what the other poster had heard and thought it was the takeoffs, rather than the crashes?)