Yes, allowing Boracare to freeze can make it ineffective. It should be stored in a controlled temperature area out of direct sunlight and extreme temperatures. You also want to avoid applying any product in below freezing temperatures because the water part of the mixture can sparate and freeze.
Yes, after the Bora-Care has dried, you can sand and finish the wood. It usually takes 24-48 hours to fully dry.
Wood just needs to be dry before applying Bora-Care. It can take up to 48 hours for it to dry after application. It should dry clear when mixed as directed and would not affect stain once dry.
Bora-Care will take up to 30 days or more to penetrate all the way through the wood and eliminate a drywood termite colony in the wood.