I am doing this tour in February 2022, and we have lots of experience with Disneyland over the past 15 years (west-coast Canadians who travel to Anaheim at least once a year). If you polled the Disneyland fans on these boards, then your average recommended stay at Disneyland is going to be 3-4 days. The
ABD tour includes a four day parkhopper, and while we won't get full days in the park on all four days (especially if you have to fly home on the sixth day), we are getting VIP tours which may include some preferred access to rides.
Long story short, given the free time allocated for the four days, you should be able to see everything you want to see. That said, we plan to stay Friday night which gives us the entire last day of our four days in the parks. So I think one extra night will be fine. It you aren't flying out late on that added day, you can get a fifth day in at the parks, but note that the parkhopper we will be provided with is not upgradeable - you will have to purchase extra park tickets for your added days.