Typically the safest time in the year for waivers, every team is still analyzing 3 or 4 players that they have already and deciding what to do with them, before even even thinking about assessing a player from another organization.
Also what message does it send to players in their own org? We were going to keep you up, but there's this other player we got for free that we have to keep up now, but his old team didn't need him.
Wouldn't surprise me if there wasn't an unwritten 'code' amongst GMs that you don't claim players off waivers at the begining of the season.