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For the lightest crowds, choose a Monday-to-Friday visit at opening time or in the late afternoon. Verified sources do not identify one consistently quietest weekday, but they do consistently note that midday is busier and that weekends are busier overall than weekday visits.
If you are visiting in July or August, avoid late morning and midday when tour groups can create bottlenecks. Weekend visits are manageable, but arriving right at opening time gives you the best chance of seeing the Donatello and Michelangelo rooms before they fill up.
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July and August are the busiest months mentioned in visitor reports, with the biggest build-up in the late morning and around midday. If you visit during this peak summer period, plan for opening time or late afternoon, especially if you want a quieter route through the main sculpture galleries.
For a better balance of weather and crowd levels, April to May and late September to October are the strongest shoulder-season options in the verified sources. Reviews also describe queues as much lighter outside peak periods, often minimal compared with Florence’s larger museums.