According to The Wrestling Observer, WWE officials were aware of Evan Bourne's drug test failure several days prior to the actual suspension announcement. As a result, WWE made the decision to pull the tag titles from Bourne and Kingston at the Oakland house show event, and reportedly sent John Laurinaitis to the show to oversee the title change.
At this point, it seems as if Bourne's return date would be 3/19, which could mean a serious pay cut for him should he miss the WrestleMania pay day in addition to The Royal Rumble pay day. At this point it is unclear whether or not WWE will book Bourne to appear on the WrestleMania card given that the event is so close to his return time.
As to the question of when WWE decides to suspend talent, it's being said that company policy is to suspend the wrestler, if he or she is currently involved in a storyline, at the TV taping following the Wellness Policy violation. This allows WWE to run an angle on TV to explain his absence and "tie up any loose ends."