From my records - average ~25 to a month. But I am in the north.

There are too many variables involved to give you a one-size-fits-all answer to that question.
Location; weather patterns; garden conditions; and last but certainly not least, the predilections of certain varieties.

If your garden has a good balance of early/mid-season/and late blooming varieties, I'd suggest selecting a date in the middle of that mid-season range of dates.

I just found about a 2" scape on Butterscotch Ruffles, which usually blooms about a week or so before anyone else. So I will take the conservative view and figure that BR will bloom in 21 days and any other (hopefully) in 28-35 days. I will tract the bloom on a couple and add it to this thread - if I remember!! Thanks for all your help, folks!

If the scape is down in the foliage , time to first bloom is about 60-65 days. I did a survey of my daylilies one year noting the first sign of scapes and first bloom. When I counted the pages I had written it on, it added up to that number give or take a day or so.