What is this? (Paint related)

Almost everything ive done Ive gotten a crash course in. I didnt expect this to be much different. On the P sheet for the paint they dont even give you a mix ratio for reducer. But I have emailed them to find out exactly what that is. I have about half a gallon left im going to order another quart and hardner. All I have is medium reducer. What "Ideal" weather should I shoot in?