Is there a set time of day that the prices decrease on waiver wire players?

i believe its after 24 hours on the list.

I see many players prices change at the same time, so it is't exactly 24 hours after they hit the wire. It isn't immediately after the games are played either.

The knowledge base doesn't say exactly...

The Waiver Wire can be found by clicking on GM's Office. The Waiver Wire shows players that are available to be claimed. Players salaries are incrementally reduced throughout the day, so you may find some bargains (these guys need to eat too)! You may claim a player if you don't already have that player on your roster (the same player from the same year can not be on your roster twice) and you have enough available cash to afford to claim the player. In order to claim a player off waivers, you must also release a player unless your team has an empty roster spot resulting from an uneven trade or previous release. The salary freed up by releasing a player combined with any available cash you had after your draft equals your buying power - the maximum you can spend to claim a player on waivers.