Steve,
Earlier, I would leave the knot a little loose and then I could screw it up and down the serving and adjust it a little. I would tighten the knot after I got it positioned where I wanted it. Generally, I found that this required gluing the knot after it was in its final position, as it didn't seem to be quite as tight as when I tighten it at the same time I make it.
However, I prefer tightening the knot at the time I make it, as it seems to stay tight that way without the need for glue, and makes it easier to replace than a glued-on nock. I use a loosely fastened metal nock during the tuning process, and then replace it with a tied-on nock when I know where I want the nock point to be.
The nock material does get worn after a period of use and needs to be replaced, or I might change my mind about where the nock should be located, so I do get a fair amount of practice making these things. Enough that I can anticipate the shrinkage that will take place when I cinch up the knot and so extend the wraps a little further down the serving than I want them to end up after I tighten the knot.