All I can find on it now is this:
Fall Sports: This period lasts for 30 days in the fall, beginning 7 days after your given sport’s championship selection. It opens again for 15 days in the spring, from May 1st to May 15th.
Winter Sports: These sports can enter the portal during a 45-day day period, starting 7 days after the championships selection.
Spring Sports: These sports can enter the portal during a 30-day period in the spring. This 30-day period starts 7 days after your sport's champions selection. It reopens again for 15 days in the fall, from December 1 to December 15.
Maybe there aren't two windows anymore?