I responded directly but it is almost identical to what Geoff kindly adviced.
A small cold at 0 Celcius may not damage anything, but especially thin leafed Japanese maples are easily having the leaves harmed. It will set the growth back some if the damage is severe. If only the tips are damaged it will mostly be aesthetical damages more than a horticultural setback.
Also, newly transplanted trees must be protected, as they’re more vulnerable. Especially Shohin where the roots freeze quickly in the small pots.