I check it before a ride. That's the last time until the next ride or I get an alarm which I haven't.
+1
I have always assumed (and we all know what that implies) that the 42 psi spec was a cold spec, and that the engineers at Mother Honda accounted for the rise in pressure due to operation when they formulated the baseline number. Or, turned around, maybe they worked out the target operating pressure and derived the cold pressure that would be needed at the start, in order to get to the target pressure when riding.
In either case 42 psi cold is the only number I use.