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If your clivia is rootbound in the pot you can divide it any time after it has bloomed. if you would like it to bloom next year, October is the best time to do it.  If you don't want to break the pot, saw around the inside edge of the container with a sharp or serrated knife. Force water up from the bottom hole of the container with a hose to loosen the rootball. Sit on the ground, place your feet on either side of the pot rim and grab a big handful of leaves, pushing with your feet and pulling from the big handful of leaves it should  pop out. Cut the individual plants apart, first using the knife, followed by using your hands to separate the roots. You will loose some but don't worry about it. Cut off any badly damaged or long dangling roots (more than 8 inches long). Put a piece of broken pottery over the drainage hole in the new pot (s) and fill with bagged potting soil, mix in a small amount of organic fertilizer and replant the bulbs (leaves attached) three to a pot. Put the pots in a shady area with bright light, fertilize until the end of October and keep watered as you would with other house plants. If the plant roots are not that crowded you may be able to just pull the plant out of the pot without sitting on the ground, etc..