I find it easier to make the squares (to be cut into half squares) a little larger and cut down to size.
That way you won't have to worry about the exact 1/4" seam or scant 1/4" seam. The 7/8" barely gives you wiggle room if you accidently got the seam allowance a bit larger or smaller. So if I wanted 2 1/2 squares I would then cut the square at least 3"