As far as we are concerned there is only one critical issue re minimum temperature for growing n. sarniensis in our experience. Never let frost at the pots. We endeavour to maintain at least 3 degrees C. throughout the coldest nights (and days) - it doesn't matter how warm the air becomes during the day. Try and keep the bulbs on the moist but dry side in the coldest times. One year early on we lost quite a few bulbs to frost induced rot, but quick thinking and cutting up the bulbs into scapes, using fungicide and putting into inert media meant they soon replicated again into bulblets.... phew. Too hot in the winter nights also probably not good either. The old wisdom was that fluctuations in temperature in September trigger the bud growth. The scientist in Holland who told me about the two bud research was call Bert Hennipman- it is many years now since he told me this but he can be found via google Nikko