my preference is to do that sort of trimming before fillets....just so that i can ensure i have the wood meeting as tight as possible before the fillet goes in.

you may find after the trim that you can adjust the tension of the stitches a bit to close out any little opening the trimming exposes.

the bigger the gap, the more important it is to address it prior to filletting.  but 1/2 inch is not a lot.

h

   Thanks for your response! Will do as you said. This is my first build and it seems to be going a lot easier than I thought it would be ! Loving it !