Some lists will give you a specific deadline for each issue, but many do not. You can often get a reasonable idea of lead time by checking the market guide for how far ahead they want holiday or seasonal material. In any case, it is best to send such theme-related material as far ahead of time as possible. Don’t wait until the day of the deadline to get it there. Because they will be concerned about filling the issue, they usually don’t want to wait until the last minute to fill all the slots.
Some editors want a query for theme-related material, while others prefer to see the complete manuscript. Determine which your favorite editors prefer and send them what they want. Keep in mind that your chances of selling to a theme-related periodical are almost nil if you ignore the themes. While on the other hand, you increase your changes ten fold if you study the magazine to see how they treat their themes, follow the theme list, and get your submissions in in plenty of time. Also when submitting material to fit a theme, include a cover letter identifying the theme issue you are targeting.