I've never dealt with Day lily seeds and always divided them to get more so don't take this to the bank so here it goes.
I've never soaked seeds over 24 hrs and either put them is soil or put them in a damp paper towel. Seeds need oxygen to germinate. The oxygen causes cellular respiration that breaks down stored nutrients to make energy to grow. Soaking speeds up bringing the seeds out of dormancy and softens the shell but you shouldn't over do the soaking time.
I can't see how day lily seeds would be different from other seeds, but I really don't believe three weeks sitting in stale anaerobic water they have any chance of growing. I try to get the seeds to sink in the first 12 hours, and with most seed if they don't sink I throw them away and won't waste my time on them.

I have found that some seeds will not germinate in water but must be put in soil (or whatever medium you are using--I use a seed starting mix with coconut coir). I suspect that the evergreen or semi-evergreen seeds are the ones that germinate in water the easiest. The others are probably dormant.

Your seeds have been in the water long enough to rehydrate them so go ahead and plant them. I once soaked a batch of desirable seeds for 4 weeks with no germination. Rather than throw them out, I planted them and most of them germinated.

I germinate my seeds a little differently than most growers. I do refrigerate my seeds (in little baggies) until I am ready to germinate them. When I am ready to plant them, I pour a little water (I use distilled, but I don't know if that is necessary) in the baggie and put them back in the refrigerator. I used to keep them there until they sprouted, but now I wait just a few days. This cold moist treatment approximates what would be happening to them in nature. The semi-evergreen/evergreens probably don't need the cold moist treatment, but I think the dormants benefit from it.

I would give the unrefrigerated seeds a cold moist treatment. I would put them to soak in the refrigerator and keep them there for a week or so (or until they sprout--some might sprout in as little as a couple of days). I find that I don't need to wait until they have sprouted. In fact, I prefer that they haven't sprouted because they are easier to plant. It's too easy to damage the radicle.

Another reason I prefer to soak my seeds in the refrigerator is the cold temperatures inhibit the growth of mold.

Good luck!

Thank you for the suggestions. I will put them in the fridge - then just plant them all and see what happens. Many look plump. Cant hurt to put them up - put outside to see if they come up, maybe cover with plastic wrap. Our freezing temps will be over tomorrow - and will start warming up for spring.

The ones that float are the viable seeds. The bad ones that sink to the bottom are the bad ones. Seeds that have been left out in the open air instead of refrigerated take a much longer time to sprout in the peroxide/water mixture. I would suggest planting some of the ones you most care about in a planting medium to see if they will germinate.

Debra