You can press your second freezer paper stencil on the fabric right away and continue to work. Just put a piece of plain paper over the stencil to keep any paint off your iron.
When you work “wet” (without waiting for the paint to dry) you may see some blending of colors as you apply paint with each subsequent stencil or image. If you do not want any blending, wait 24 hours between images. You can also use a heat gun or embossing tool to get a film to form on top of your paint quickly. (A hair dryer probably is not hot enough.) I would reserve the heat-gun method for cotton and natural fabrics as synthetics will probably melt.
