tips for spraying primer

If you have solvent pop that deep, you should continue sanding with 180 grit, not try to fill those holes with more high build primer. At 13C, approx 55F, if you're spraying in an unheated shop, wait at least a half hour between coats of high build.
What brand of high build are you using for the job? If you check the data sheets for your particular product, they will give the recoat times and gun pressure settings that work best with their particular product.
Also, if you haven't sprayed high build urethane before, don't mix more than a gun cup full at a time, and blow some gun wash through your gun between re-loads, just to be on the safe side. Good luck.