Yo, marijuana plants have been known to survive in 33+ degree weather, if you take precautions they should be good. If you lay a blue tarp over then that will keep temps out a lot. They look to big for trash bags. Some people pull at the second frost, but if that is in 3 weeks then they might not be done. If it is 40 degrees, I would say fuck it, they look huge, meaning they have a root system about as big to a little bigger than the plant, sooo I doubt your plants roots are going to "freeze". The thing about the cold, is supposidly if they are still developing, temperatures jumping at night can lower thc levels. I have heard it can discolor your plant too.
Now that I am looking at them again, some of them might be small enough for trash bags. Anyways try your hardest not to pull because of frost, unless it is a necessity, say it gets to 0-25 degrees Fahrenheit.
Forgot to add, it pisses me off when people pull for a little frost, Ive seen pictures of marijuana plants covered in snow, then pics of the snow dug out right after it happened. These guys were to high to watch the weather channel, and they lived in BIG BEAR CALIFORNIA! These plants (OG OG) survived 6 nights of frost (temps of 30 degrees...) Do whatever you want... I am just saying, these plants are tough as fuck.
(which is what years of selective breeding have done)