I'll repost here what I put in the other thread about what I learned:
Throwing this out there for anyone (like me) who was a little confused about the IR return process.
1) Once player has been put on IR, they can't even start practicing for at least 6 weeks.
2) Once 6 weeks has gone by, the team can choose to have a player start practicing.
3) To be able to start practicing, the team must use a "designated to return" slot on the player.
4) The team can wait as long as it wants to have the player start practicing. There's no "use or lose" deadline with respect to the start of practice.
5) However, once the player starts practicing, the team has 21 calendar days to either activate the player to the 53-man roster or decide to leave the player on IR. And as we know, if the team decides to leave the player on IR, the team does not get the "designated to return" slot back.
6) There's no minimum practicing time. A player could be reactivated immediately
6) However, a player must be on IR for at least 8 weeks. So if they were to start practicing once the 6 week clock expires, they can't be reactivated for 2 more weeks. But if they start practicing 8 or more weeks after being placed on IR they can be reactivated immediately