I think that you should look for this answer in Chapter 5. This is the first time that we meet her in the book and the author sort of introduces us to Miss Maudie and tells us about her. The author does not come right out and say "her favorite pastime was..." but you can infer what her favorite pastime is from what it says in the chapter.
If you look in there, it talks about how much time she spends on her flowers. It also tells about how she treats fighting weeds as if it were the "Second Battle of the Marne" ( a big battle in WWI). From that, I would infer that her favorite pastime is gardening and/or taking care of her yard.
As was mentioned in the previous post, Miss Maudie's favorite pastime is working with her flowers outside. She is continually gardening throughout the novel and taking care of her azaleas and various flowers. Scout mentions that Miss Maudie hates staying indoors and works in her flower bed until five o'clock each day. Miss Maudie is friends with the children and allows them to play in her yard, as long as they don't run through her flowers or climb on her arbor. Scout also mentions that Maudie loves anything that grows from God's earth, except weeds. Scout compares Miss Maudie's campaign against nutgrass to the Second Battle of the Marne, a famous World War I battle. Miss Maudie even continues to garden while the foot-washing Baptists make derogatory comments to her. Miss Maudie's favorite pastime is gardening in her flower bed.
caring for her azaleas.