If you've played Season 1 it's almost out of time to collect all the rewards up to Level 50, so make sure to grind before Season 2 is released if you're missing one or two of them. More information is available here on the exact date Ultimate Season 2 will arrive in Madden 22 and what kinds of content will be included.
Madden 22 was released Ultimate Season 1 with the launch of the game even though it technically was accessible as early as August 12 due to EA Play Trial, EA Play Trial, the actual date for its launch was set for August 20 in 2021. Last year, we saw every MUT Series last between 30 and 40 days in average, it appears to be significantly more extended this year.
While an end date has not been officially announced, EA stated in the build to launching Madden 22 that the new Ultimate Season model would aim to keep each Season running for approximately 90 days. Already, they've dropped 1st Challenges in 2nd Quarter and 1st Quarter in Ultimate Season 1, with 3rd Quarter as well as 4th Quarter challenges due to drop in the coming weeks.