I sure do miss senior hours, at Costco and elsewhere. The lack of crowds, restriction of numbers of people per cart (I know it's a family fun time, but they do crowd the aisles), fully stocked shelves, fast checkout, and just general quiet was great and more than made up for the lack of samples. Most of the grocery stores I frequented had senior hours but did not enforce.
I suspect that late afternoon is now the best time, but it doesn't fit my shopping style. I haven't yet found a consistently good time. If you hit it just after opening, it can be good, but if delayed even 20 minutes, it fills up.