There is a stage in the 'Approval Pending' range, where all Peer Reviews are in, and the track is in quarantine to allow HMX the opportunity to check feedback notes and do their own verification.
We've already seen that tracks will go up for sale earlier on the xbox.com marketplace site, but are delayed for the in-game RBN Store. This is partly due to the fact that HMX will assemble the list for what's released on a given day by hand (or at least 'under editorial auspices'), linking up the offer IDs to the DLC in question.
As such, I don't think it would be any great feat for an author to email HMX and say, "Hey, that one track approved today? Can you hold it 'til next Tuesday? Thanks!"
Of course, it'll still be available at xbox.com before that, as part of the automated XNA process, but it might help your press-blitz a little to sync at least one channel to the announcement.