We don't regularly get heat that high; our average summer daytime temp is more like mid 80s, but we do get some hotter days (high 80s to mid 90s, and infrequently into the high 90s). So I don't
have to shade plants, but as my property is full of oaks (and other trees), partial shade for my daylilies is mostly unavoidable. (There are a couple of planting beds that
may get full sun (or close to it), but the daylilies there have to share the sun with other ornamental plants.)
My only comment on partial shade is that while the daylilies grow, and bloom, they may not rebloom. ('Green Dolphin Street' regularly rebloomed for me at our old house, where it pretty much got full sun. It does not do so in the partial shade bed at my current home.) I suspect that may depend on the individual cultivar, though.
(For what it is worth, I also have some suspicions that shade may factor into the percentage of polymerous flowers a daylily has - though in the particular case that follows, water may also play a role. I had one seedling which in its original raised bed ran about 25% polymerous. I dug out that bed entirely (I am using it for veggies now (it was never sprayed with fungicides, herbicides, or pesticides as I don't do those)) and potted the seedling. The pot possibly (it is hard to quantify) gets a bit less sun than the bed does - and that seedling, after the first year in the pot, has not produced another poly bloom.
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