Fruit trees develop cold hardiness, or the ability to tolerate low temperatures, with exposure to freezing weather. As the weather warms up they lose this cold hardiness which is why early spring frosts can be detrimental. The cold weather we have been experiencing is not harmful since it followed progressively lowering temperatures. Damage to fruit trees typically occurs when the weather fluctuates rapidly from warm to extreme low temperatures. Fruit trees that were not pruned properly are at a greater risk of damage from the extreme cold as well.
As fruit trees begin to set buds the cold hardiness varies. This chart from Washington State University reports the temperatures fruit trees can withstand during various stages of budding. https://treefruit.wsu.edu/article/critical-bud-temperatures/