Try to find a small fan and keep air flowing over it. Don't put the fan right up next to it, but close enough where you can feel air moving by the model. If you try to speed up the drying time to much, the surface will dry and then soften again as the solvent underneath continues to bleed off. If you can smell any solvent, it isn't dry
Is it possible you laid down too thick of a coat in one go? if that is the case, unfortunately you will just have to be patient. 48-72 hours is not an uncommon time to let a basecoat dry, especially during the winter months.
That old Testors square bottle enamel is some slow drying stuff. I try to avoid it whenever possible.