Mr. Willis,
As far as I know, from my dealings as vice-chair of the Solder Mask Task
Group, no such reliable test method exists.  You might look for a method
which examines the change in capacitance with curing time.  I saw a
demonstration of it a few years ago, but never had the opportunity to pursue
the science.  The basic theory is that an uncured solder mask is applied over
a test pattern and the resistivity and capacitance are measured as the cure
cycle goes along.  When you have reached a point at which the two values are
only nominally changing, you have reached full cure.
I wish I could be of more help.  I guess memory is the first thing to go.

Doug Pauls aka [log in to unmask]
Contamination Studies Laboratories.