While the paste is on:
Leave the henna paste on for a minimum of 4-6 hours, longer if you can. Designs done in the evening can be kept on overnight.
To prepare for sleeping: be sure the paste is completely dry, dab with sealer, then wrap with some toilet paper and tape it up. You may want to slip a snug sock over the whole bit, so it doesn't come unraveled in your sleep.
Try to keep the hennaed area warm. If you feel chilly (henna is very cooling), place a heating pad, or hot water bottle on your dry/wrapped design.
Remove the paste:
Pick with your fingernail, or scrape with a credit card. Rubbing in a little olive or coconut oil will help to soften the paste for removal. It's important to keep the new design dry. Don't use water to remove your paste!
After you remove the paste:
Your design will be a bright orange color when the paste is first removed, but it will darken to a brown/red color about 36 hours from the time the paste was applied.
Keep stain dry for the first day:
Water on the design in the first 12 hours will inhibit the darkening process. After that, you can bathe normally but stay away from harsh soaps and scrubbing. You can protect your henna stain with olive oil, coconut oil, and other natural body butters when bathing.
Things that will shorten the life of your design are: hot tubs, swimming pools, washing with strong soaps or exfoliates, and vigorous scrubbing.
Moisturizing will prolong the life of your stain; just use a little cocoa butter or coconut oil.
Designs last for about two weeks; about one week of strong color, and another week of fading.