Really depends on the USB drive your using. I use a flash drive with ~200MB/s read speed and I was able to install windows 10 to an SSD in about 7-10 minutes. At least it felt like it was that quick. If you grab the latest .ISO from windows there should be minimal updates.
It's really dependent on what it's reading from and what it's writing too. With a basic thumb drive and a typical HDD it may be anywhere from 20-40 minutes I suspect. I haven't installed to a HDD in a while.