For the record (and for Sharon) I contacted Rust-oleum regarding their Painter's Touch primer, which is what I used on my plastic pot. This was their very prompt answer:
"Thank you for contacting Rust-Oleum Product Support.
If you are using our Painter's Touch Primer brush on version, you are able to top coat with an acrylic paint after 24 hours. If you are using the Painter's Touch Primer aerosol version, you will be able to apply an acrylic based paint after 3 days. The Painter's Touch brush on primer would not be ok for plastic but is ok for metal. The Painter's Touch aerosol primer is ok for both plastic and metal. We hope this helps. Please do not hesitate to contact us if any additional information is needed."
They definitely get points for their almost instantaneous answer (just over an hour!). I used the aerosol primer and it's very nice to use; covers much more quickly than some of the other spray paints I've used.
