Certain week days have special activities for specific Friends:

Tuesday
Two's Day for Pooh. All the honey values are doubled on Two's Day.

Thursday
Sandwich Day for Stitch. On Thursdays, Pudge the Fish is at the beach. If Stitch feeds Pudge a peanut butter sandwich, Pudge will make it sunny if it is raining; or rainy (or snowy, depending on the season) if it is sunny.

Friday
Dung Day for Simba. He gets extra dung beetles in his Bug Harvest competition against Timon on Fridays.

Saturday
"Fish Are Friends" Meeting Day for Dory. The "Fish are Friends" meeting takes place in the Sunken Ship location.