I usually do up the seat tube/top tube junction first, and then finish it before putting the front triangle back into the frame fixture to put on the rear end. The fillet here gets done in bronze, and the seat stays are put on with 50N silver. This makes doing finish work a bunch quicker and the silver has a much lower melting point than the bronze, so the finished fillet will not be disturbed by the heat from brazing on the seat stays.