After a fluoride application, can I really not brush for several days?

No, you do not have to go without brushing for days. With a standard fluoride application you only need to avoid food and drink for 30 minutes to an hour, and you can brush as usual from that evening. However, if a sticky varnish-type fluoride was applied, hold off on brushing for about 4 to 6 hours so the fluoride can soak into the teeth, and avoid hot or hard food that day. Having fluoride applied regularly, usually every 3 to 6 months, helps prevent cavities.