The length of time depends more on the product than anything else. Some product labels instruct you to wait a certain amount of time before buffing off.
The other factor I keep in mind is humidity. If it's really humid, I let the wax sit on longer before buffing. I always let sealants dry for at least 30min. Sometimes I'll let it sit overnight if it's not going to get near the freezing mark. I did that with #16 a couple weeks ago, and had no problems with it.