Recent question was whether you had to re-coat within 4 Hrs or wait 6 weeks which was what Finnegans used to print on the tin. The official answer from Akzo Nobel Technical is:
"The formulation of the Hammerite Direct to Rust Metal paint has changed from xylene based to white spirit based. This means there is not a time restriction for application of the second coat so you can do this anytime from eight hours of application of the first coat."
This would also mean that no need for expensive Hammerite thinners anymore - white spirit could be used - though they didn't say that.