The data is now searchable in Have I been pwned (yes, all 359,420,698 unique email addresses) and if you do find yourself in there and know when your account was created, drop a note in the comments below and we might be able to crowd source a more accurate picture of when this event occurred.
Update: Since writing this piece, My Space have posted a blog about the incident which they've dated as having occurred before 11 June 2013.
That's not to say it couldn't have been hacked in a more traditional external-actor sort of way, but the timing is coincidental...
So that's the best estimate I can draw on the evidence here - My Space was probably hacked in the mid-2008 to early-2009 time frame.
Going back to another recent large incident, here's how the data on Linked In breaks down: This is obviously a really different split; Gmail is now well and truly out front which is more commensurate with what we'd expect today.
Keep in mind that Linked In was hacked in May 2012 so now we have a window somewhere between then and 2007.
That's right, truncated and case insensitive passwords stored without a salt.
One possibility that would explain the ginormous volume of data that was taken (the extracted breach file is 33GB) is an insider threat.
Keep in mind that we're talking about a time where My Space was running into serious trouble and there were a raft of lay-offs, it's highly conceivable that someone literally walked out the door with the data.
However, it wasn't losing and you could speculate that they could have been frozen in time in 2008 then hacked years later and the evidence would still point to the incident occurring 8 years ago.
It may be that the incident occurred after 2008, but I doubt it was much later as they were still getting registrations and they would have been very heavily Gmail biased by that time.