I was just wondering when it comes to the official date to start 2-A-Days, what is the date?

I heard that you could not start until August 1st and I have also heard that you can start the week of the 1st. Like this year, the 1st is on a Wednesday so from what I understand a team can start 2 a days in July 30th. Just checking b/c I have heard both ways and I thought it was the latter being able to start on the 30th b/c the 1st is in the middle of the week.