As long as the epoxy is warm, this is okay. When laying epoxy in cold weather conditions, in an unheated garage, for example, make sure it is kept off the cold concrete floor or placed over mild heat. Once you have finished the job for the day, place the bottles in a box and store them in a warm place; an airing cupboard or boiler room would be ideal. If the weather is extremely cold and you are working in a shed with no heating, for example, it is best to warm the wood with a heat source instead of trying to heat the entire shed.
The trouble with epoxy resin is the fact that it becomes viscous when exposed to the cold for any significant period of time, and it will eventually crystallize. As a result, you will find it tough to dispense, and mixing it will be a significant challenge.
If this happens, you need to be patient when bringing the resin back to a useable state. This can be achieved by warming the bottles and contents in a process that takes several hours and is likely to be extremely frustrating. It also means a great deal of time can be lost on a project if you only have a few hours at a time to work. The best method of heating the epoxy resin is to place the bottles in hot water.