I have witnessed hummers sipping on my daylilys as well as many other blooms you wouldn't think they would use. Having seen what I have seen with my own two eyes and repeatedly, I have to say this business you read or people say about they only nectar from certain shaped blooms is pure, outright bunk.
I think that the more blooms you have out there, the less you might see them at the feeders. They really do prefer "the real thing" as opposed to the sugar water we give them. Sure they use the sugar water but it's not their first & foremost choice -- at least from what I've witnessed.
Ibis, I think it matters too, just how many hummers you have in your immediate area. If you have 1 or 2 & there's lots out there for them to nectar on, then they may still visit your feeder but quite infrequently. The less frequently, the less you're apt to happen to catch them in the act.
If you had a population explosion, there's more competition & thus they can't each get as much from the blooms so will frequent the feeder more often.
I say keep the feeder up the rest of this year. It can take time. Then put it up next year. If mid season you don't see any then take it down.