I ran a Tillotson 334AB, very similar to the HW27 with a smaller venturi. I generally replaced full kit every 3 or 4 hours of run time. I would occasionally check it every 2 hours of run time, clean and blow it out, but the diaphragms didn’t start to sag until the 3 or 4 hour mark. They were OE kits. Aftermarkets may not last as long.
This is a pretty good guideline. For heavy racing or bigger competition, we generally recommend changing the diaphragms and gaskets after each race weekend, but for more casual use, every 2-4 races is fine. And, yes, check them at intervals and if they are sagging or deformed, replace them. The “DG” kits with just the diaphragms and gaskets should be fine for that sort of maintenance. You only need the full “RK” kits you referenced if the needle and seat aren’t holding pressure or are damaged, but we do recommend a full RK replacement once a season in any event.
Btw. Last time I was on the track, one of the racers told me to do a popoff on the inlet, after end of race day, to take of the “pressure” of the diaphragm. Is this true, and does it do a difference.