It's been ages since I used Dullcoat, but I have used similar products over acrylics, and I seem to be one of the paint gurus, hereabouts.
You should be fine provided you did your surface prep before applying the Tamiya paint (acrylics are unforgiving of uncleanliness) and you allow the acrylic to cure thoroughly before applying the Dullcoat. "Cure thoroughly" means three days at room temperature, minimum, IMHO. Of course, you can also heat cure to speed things up.