One of the most common questions I get regarding book displays is how long they should stay up before they are changed. My usual answer is no longer than a month because after 30 days, your patrons will likely have seen it and will stop looking at it. As I have mentioned in presentations, you should archive the titles on your website so that patrons can locate titles they viewed but didn't check out. It also allows patrons who are interested in the theme to see the full list of titles that were included.
To address scheduling more broadly, it's a good idea to outline your book displays at least several months in advance. Create a monthly schedule as part of a larger plan to market your collection which includes what themes for book displays and book lists you will use. Between your programs, major holidays, and local events, you are already scheduling much of what happens at your library each month. Adding book displays to this schedule will allow you to better leverage their ability to market your back list while also helping to promote your services and programs.
When I worked for Barnes and Noble, each store received a monthly marketing plan which outlined which displays and initiatives were in play for the month. Most libraries create monthly programming calendars; the next step should be add a monthly plan to promote those programs, your existing services and databases, and your backlist. Take book displays seriously and use their ability to put your backlist front and center to increase overall circulation and introduce your patrons to the depth and breadth of your collection.
You can start with a spreadsheet or form that details what programs, outreach, and initiatives your library will be involved with for the month. Add any holidays, cultural heritage observations, local celebrations, or commemorations. Note any ALA celebrations that you will be observing. That should be a good start to plan your book displays. Include the location for each display as well as which staff member or department will be responsible for setting up that display as well as keeping it full.
As you work with your monthly schedule, you can make adjustments as necessary to meet your library's needs.