Every wax will be different when it comes to layering. I use a harder wax that works great for layering. A good starting point would be to let the wax completely set up. If you find that your wax pulls away from the mold and the second layer is bleeding into the bottom layer then try pouring when the mold has cooled. If you're still having problems just keep shortening the time between layers. Don't forget to keep good records. If you're not getting a clean crisp line, a trick I've learned for the second layer is to pour a thin layer let that completely set up then finish the second layer. This works great when making red, white and blue votives.