The deadline for "non-waiver" (unrestricted) trades is 4 PM (Eastern) on July 31st. No trades can be made between 4 PM and 5 PM (Eastern) on July 31st, and then beginning at 5 PM (Eastern) on July 31st and extending through to the conclusion of the MLB regular season, Trade Assignment Waivers must be secured before players on MLB 40-man rosters can be traded. (Waivers are never required to trade a player on a minor league reserve list).
If a player is placed on Trade Assignment Waivers and is not claimed, waivers are said to be "secured" and the player can be traded to any MLB club at any time, just like prior to the non-waiver trade deadline.
Trade Assignment Waivers are revocable the first time they are requested on a given player in a waiver period, so if a player is claimed, the player's club has the option to either withdraw the waiver request and retain the player, or allow the waiver claim to stand. The player's club has 48 hours to make this decision, and during this "window" the club has the right to trade the player to the claiming club (but ONLY to the claiming club). If the player is not traded to the claiming club before the window closes, and the player's club chooses not to withdraw the waiver request, the player is automatically assigned to the claiming club for the $20,000 waiver price ($25,000 for Draft-Excluded and Rule 5 players) and the claiming club assumes 100% of the player's contract. (A player with a "no trade" right can refuse both a waiver claim and a trade assignment, however).
If a player is claimed but not traded and the waiver request is subsequently withdrawn, the player cannot be placed on Trade Assignment Waivers again for at least 30 days from the date the waiver request is withdrawn, and if the player is placed on Trade Assignment Waivers again before the end of the season, the waivers become irrevocable and cannot be withdrawn. A player who has a "no trade" right (full or partial) cannot be placed on Trade Assignment Waivers a second time before the end of the season unless the player first waives his "no trade" right.
Trade Assignment Waivers secured on a player on Optional Assignment to the minors or on an MLB Disabled List expire after 72 hours.
If a player on an MLB Disabled List is placed on Trade Assignment Waivers, he must be eligible to be reinstated from the DL and healthy enough to play. If waivers are secured, the player must be reinstated from the DL within 72 hours. If the player is claimed and the waiver request is subsequently withdrawn, the player must be reinstated from the DL immedialtely.