How to store Reta

I just ordered by first ever 10 mgs today, I’m really excited to start but I have an upcoming vacation in a few weeks and am a little hesitant to start injecting until I get back in case I have negative side effects that ruin my vacation. When it arrives to me as the powder and liquid, should I combine it immediately then just leave it in the fridge? Or should I wait to combine it until I get back and am ready to start injecting? Also do both the liquid and powder go in the fridge before being combined or just 1? Thanks in advance