I had bagseed outside through several frosts, they were fine. It depends on the genetics of your plant and observation of how she does when it gets cold. In NY state I put out some plants last year very early, like April, they survived several frosts but a few turned male. Sometimes the stress of weather can turn them hermie or male.
That is 51 degrees farenheit, they will be fine, even a fragile seedling would be fine with that. Keep in mind, most bagseed is of a mexican hybrid variety and my bagseed were fine with 32 degrees farenheit.