I skipped over most of this thread but someone explained that real enamel
has a narrow window for re-coating, and that it will wrinkle if you miss the
window. Rust-O-Leum itself points out that the re-coat window varies
*widely* on their different products. They have a lot of information on
their website.

From the Rustoleum site:
"
Strong solvents can also soften a previous finish and make your new paint
application susceptible to wrinkling.
"
and
"
If you sand in-between coats, allow the full recoat time to dry before
applying another coat (at recommended drying temperature).
"

So I guess sanding after 24 hours exposed not-yet-dried paint and the alcohol
softened it further.

So recoat within 1 hour or wait 48 (as the can says...).

Thanks to all who contributed to my education. :-)