It probably would prolong viability if you could do it without killing them, which requires them to be dry enough (which would take more like a few weeks air-drying rather than days). In Griesbach's experiments hydrated seeds died at freezing temps that were less cold than a domestic freezer while dry seeds survived much colder.
So, why do they survive outdoors over winter? A couple of thoughts there - nature is interested in the survival of a species as a whole rather than an individual. So if 100 daylily seeds fall to the ground, 30 survive and 25 germinate then the species continues. As a hybridizer you want better than that so you want them all to survive!
If losses in nature are actually not high from freezing over winter then perhaps the seeds survive freezing because they dry down sufficiently while laying on the soil surface after falling. Or, maybe it would be the gradual lowering of temps that causes them to increase their freezing tolerance similar to whole plants.
A daylily plant survives temperatures colder than freezer temperature every winter here (although air temperature is likely to be colder than soil temp) because it has time to "cold acclimate" as it gets gradually colder in fall. Put that same daylily plant straight into a freezer in July and it will die. Does this apply also to seeds? I don't know, but whatever the reason hydrated daylily seeds placed in a freezer will most likely die but if they are dry enough internally they may well survive.
