It's not the drying out that might cause cracking. I've posted that iron x is essentially an iron limit test in chemistry terms.
If you break it down physically, iron embedded below paint surfaces but which is still accessible to the iron out.
Limit Test of Iron - Web Formulas
If you look at the chemical reaction there's a couple things going on which just send some red flags to me. First is that the ultimate byproduct is hydrogen. This can cause either hydrogen embrittlement of materials and also some intermediary steps would be ferrous sulfates or other iron compounds. Sounds harmless but those iron compounds are physically larger than the iron molecules themselves causing physical expansion of the iron particle, this combined with the hydrogen embrittlement caused by the 2H+ ions can possibly cause paint to crack.