Schluter Outside Corner Edge - World Culture

Ok so my daughter’s original plan was black grout for the 4x12 subway tile surround with 2” black hexagons in the niches, so I suggested black Schluter Rondec to edge the niches and on the outside corners where the walls kick out outside the tub. Figured it would all flow together and look cool... Install the Schluter trim first so it will be perfectly plumb and in the right place.

Then run your tile from it to the inside corner wall. You are using a 1/2 1/2 break. On 24" tile, I like to use 1/3 break, but it is a preference. Start your tile with a full one, then a half one, etc.

Schluter Outside Corner Edge, The cut at the wall will be whatever it is. Planning to go 3/4 of the way up the internal window with schluter trim around the perimeter. Feeling stuck or cornered that I need to make precise measurements up the wall, cut and install schluter trim before i lay the tiles. Is there a trick to install the trim after the tile goes up?