We will be traveling to Florence this May immediately after spending 5 days in England. How far in advance can we make reservations for these two museums? It would be great if we could make them online before we leave home.
You can make reservations before you go at the official websites, or if you will spend three or more days in Florence and plan to visit lots of museums, check out the Firenze Card (72€ for 3 days); you can wait until you get there to buy the Card.
Check the websites now. Reservations are likely to be available now.