hmmm i never really thought about it, but I think it's okay to draw them in advance! You can take it as a themes or a daily art or writing challenge :DD Heck even I plan on drawing some in advance just so that I don't accidentally miss a day (like last year huhu) >:)) lots of people tend to repost old works too if they have pieces that suit that day's theme, and a few people asked me to post the theme much earlier so they can plan or start their piece in advance! Feel free to draw at your own pace, whether it be advance or on the same day (^v^)