Neither of us answered your question, did we?!
Here it is:
With your CPES, you got some paperwork. (I hope you didn't throw it away!) At the bottom left of one of those sheets is a CPES full cure time chart that lists how long you need to wait, according to the formula you purchased (warm weather or cold weather formula) and the temperature in your area. To be safe and not waste your hard-earned money and efforts, I would wait until you have reached the full cure time, based on that chart; then, check the thickest area with your finger to be certain it is dry. After that, try giving it that light sanding (100 grit). If that goes well, you're ready to coat the bottom of your trailer with the black goo. !
If all else fails or you still aren't certain, please call or email the Rot Doc. He will be happy to give you the answers you need.
PS. I don't remember for certain but I think that if you plan to add another coat of CPES on top of the two you've already done, you can do that as soon as what you have on there is reasonably coagulated so that the new coat will stay put and not run off. However, your best bet is to check with Doc. Rot. (206) 364-2155 or
[email protected]