Hi Frank,
Mostly this little 'project' is idle curiosity on my part. I think the plasticity of the day bloomers has never really been explored. Just in my little attempts at selecting, I've seen one grow and bloom steadily in 80% shade and now this one. Water temp was 46F this morning and it still edged another .25 inch towards the surface.
But again just playing as I amuse easily.<g> I see big potential problems trying to market a lily, the 'improvements' of which are intangibles ( visually anyway).
But to answer your question. Underwater growth of a lily and its buds is going to be largely independent of air temps...except as they obviously affect water temps. There is a native population of N. lotus growing in thermal springs in Hungary(?), an area far to cold to grow native trops, let alone a heat loving night bloomer.
I have no idea what your water temp would be during the day, but in a greenhouse it is for sure to climb and in a small volume of water I'm thinking they get real warm, real fast. My covered ponds are 21' X 6' X 18" and the water temp rises 15 F on a sunny day. Of course, you will also lose heat more quickly once the sun goes down.
But all in all, your water temp is obviously getting warm enough, long enough to form buds. And for reasons I can't fathom, vivips do seem to be more cold tolerant. Once the bud hits the surface, it is at the mercy of air temp as to whether it opens or closes. Many times in the cold if they do opend, they never close. More common in what I see, is the lily tries to pull them back down ( they get the "S" as though the pod is fertile) until the air temp warms enough to support a bloom.
