In this brief guide I will share my understanding of the calendar puzzles, and how to solve them. I hope this helps anyone who also struggled.
A Few Calendar Solutions
Understanding the solutions
I start by finding two of the same stickers that are already on the calendar. Then I count the boxes between them. Example 1, if there are two of the same stickers on day 4 and day 18, then the gap is 14 days. Once you get that number (each number is different for each puzzle) you continue to make that gap for all stickers. Focus on adding to the calendar date, but you may need to go backwards to. Example 2, two stickers are on 30 and 17 but you need to place another. The gap between 30 and 17 is 13, just place the last sticker on 4.
For a visual step by step here is how I got the solution for level 12 in Chapter 1 Home Sweet Home
I counted the days between the blue flowers. The first blue flower is on day 4, the second flower is on the 13th. With that knowledge we know the gap is 9 days.
So to finish the pattern I put the next blue flower on the 22. Now just continue the 9 day gap for all the stickers.
This is the full solution
Good luck! I hope this helps