How do I use temporary solder mask to protect contacts from conformal coating?

If you think of spot mask as basically liquid masking tape, the application become more intuitive:

Apply the mask to the contact areas to protect. Allow mask to fully cure.
Apply the conformal coating.
After the coating is dry to the touch, but before it is fully cured, peel off the mask. Otherwise it could create a cracked, ragged edge, or even pull up the coating.