CBS IR is horrible, but it works. 2 options in CBS for IR.
Option one is a free for all, any player can go into the IR slot, even if he has no injury at all. It doesn't even require an injury symbol next to the player name, the owner can move him to IR to make room at any time even if the player is perfectly healthy.
Option two is only players who have been given the IR tag by the actual NFL team can go into the IR slot. Option 2 means 8 weeks minimum, and I believe each NFL team only gets a single IR designation per season.
It seems as if CBS designed IR for keeper/dynasty leagues and isn't very functional for redraft leagues.
We allow owners to use the IR slot once per season, but it has to be monitored by the commish because it's easily exploitable.
Hope that helps, I've had several support tickets to CBS to clarify how their IR commish options work and this is the conclusion after having it explained by their support staff.