The touchstone process can layer up to 2mm of ink and varnish. Braille on ADA signs is less than 1mm so I suspect you would have no problem printing compliant signs.
Once layered and cured, it holds up well. We tried to pop them off with our fingernails and could not. With a screwdriver you probably could but hardly a concern in practice.
We don’t print them routinely, but we have a few we did during training.
As for as the time is concerned, their samples have the print time and ink usage so you could extrapolate a 4x8’ print time. If you do a lot, I would ask them to print a four inch sign repeated over 8’ width and time it.