Someone else may chime in, but I think your extreme fluctuation between day and night may be too much. I do callas and have done cannas in a heated garage under lights and they still take a while to get going. Growth is very slow and I have the callas on a heat mat. My thought is the fluctuation would stress them and or cause really slow growth.

If you can start them indoors w/more consistent heat, I think they'd be happier.

I agree with the above. Much better to bring them in the house where the temperature is more stable. Until the plants you mention have roots well established they are very prone to rot and other damage with those temperatures. Al

I think you are confusing heat with temperature. How would you like to spend your days in such 100ú environment, and then try to to stay warm enough to fend off freezing nighttime temperatures.

No, plants have distinct preferences and while some houseplants really go for cool nights, they would not appreciate being given the cold shoulder.

Much better to give them the temperatures they do best in--usually in the range of 60ú at night, and sunny/partial shade periods during daytime hours.

Your greenhouse should have a method to allow outside temperatures to moderate the inside heat and vice versa.
Through window glass the sun can increase dramatically on a tender leaf. A method of shading should be arranged on those exposures where the sun raises the temperature so high is prevalent. Where shade might be too much, simply raising the plant might solve the problem.
And water never solves a heating problem--water only as the plant can use it.

not really your question, but how about posting over on a greenhouse forum for a way to stabilize your temps a little? It might be as simple as throwing down a bunch of gravel or getting some water tanks to store the heat a bit.

I'm also guessing you use your greenhouse successfully to grow other plants. If they do well enough with the ups and downs then I see no problem with potting up a few of the other bulbs to put in there.... just use plenty of soil to insulate the bulbs a bit.