There are subtle differences in how long the drug works and how quickly it works. Levitra works a little longer than Viagra. They both take effect in about 30 minutes. With Levitra, the effects last for about 5 hours. With Viagra, the effects last approximately 4 hours. Cialis works a bit faster (within about 15 minutes), and the effects last much longer -- up to 36 hours in some cases. Stendra can start working in as little as 15 minutes and last up to 6 hours.