My babies have been in a hoop house with the min temp set at 60. Some days it can get up to 90 in there. I want to start to wean them off of the heater. How cold is too cold for them? What is the best way to acclimate them to the cold and lack of humidity? I was thinking of killing the heater during the day for a couple days, then less and less at night. In a week or two we'll have night temps 45/50. Is that still too cold for them? I'm thinking once the temp is ok then I can worry about acclimating to the lower humidity by opening the cover a little more each day. One problem at a time. Any thoughts?

If you can, I would say open the plastic during the day, not completely off, and keep that up for a week combined with what you already said with the heater and you could probablly start to take the plastic off for a couple hours a day for a few days then longer and longer etc if it's not too difficult.

Can't really tell from the photo how big your figlets are.  After starting my cuttings then transplanting to 1 gallon nursery pots I moved the pots outside after less than a week.  I wanted to give the cuttings some time getting used to their new home (1 gallon pot) before putting them outside.  My night time cut off is 40F.  If the temp is predicted to go below 40F at night the figlets come in.  With my very brief experience with figs, I think you should be OK with 45/50F.  This is my first season with figlets so you may want to get some other opinions from more experienced members.

The cuttings I potted up went from constant 65 inside to outside with a 45 degree overnight low cutoff. I also put them out several times in the morning when it was about 28 and the weather was forecast to warm up into the 50's, calm and sunny. 3 of the 4 outside ones seem to be doing better than the ones that I've kept inside in cups. The one that isn't doing well is because the roots were not as developed as I thought and the root ball fell apart transplanting so I can't attribute it to the cold.

Depends on how precious that cutting is. All mine, tho most are rather common varieties, are precious to me. Until outside low is above 50, they stay in the garage.

Let the be. Let them grow. Let them thrive. If you shock them when they are small, it takes time and effort to get them going again. Trying to acclimate them to the cold, in the spring is backwards. If you want to drop the temp in the greenhouse to 80F or take measures to keep the greenhouse from overheating, fine, but 90F is not a problem for small plants. 45/50F says "fall", "go dormant".