Troop Committee Advancement Chair here.
It actually sounds like you are talking about a scoutmaster conference, not a board of review. There is a common misconception that a scoutmaster conference happens when all of the other requiremens have been completed, and right before the board of review. This is not the case and it can happen any time since the previous rank was earned. If this is a new scoutmaster, is he trained? He may not know exactly what he is supposed to do but not want to admit it. I guess in this case, did your son call for an appointment? I know of scoutmasters that only do SM conferences on camp outs or on Sunday afternoons, which is a little weird in my book but not necessarily wrong, as long as they are getting done.
Now, if we are actually talking about a board of review here, that is something different, and something that the scoutmaster isn't involved in. It should be arranged by the troop committee advancement chair, or if there isn't one, the committee chair or their designee. I do this all the time. My youngest just had his tenderfoot BoR last night, but I had to quickly train an extra parent because there were not enough committee present. Usually, the only reason a board of review is delayed in our troop is if we don't have enough adults to hold one.