You can do it either way. When I used to use CBU's (only Ditra now), I would tape after the board was installed immediately if time allowed. Some people seem to have trouble with this method because they create "speed-bumps". So they prefer taping as they install the tiles. I don't like that because the tape gets disburbed when troweling the thinset.
What kind of room is this, how large? What type of tile? Ceramic, porcelain, natural stone? What type of adhesive are you using?
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.