the DL

[io]

does anyone know when teams start placing players on the DL? ... do all the transactions happen at the same time (same day) ? or different times during that week?

[GotowarMissAgnes]

They can do it any time they want. There are certain rules about 40 man rosters that make it less necessary to put guys on the DL prior to the season starting, so many teams just don't do it until it's necessary. And transactions can happen at any time during the season.