Adams's prediction was off by two days. From the outset, Americans celebrated independence on July 4, the date shown on the much-publicized Declaration of Independence, rather than on July 2, the date the resolution of independence was approved in a closed session of Congress.
LSD effects usually last for 12 hours. But LSD can stay in your system for up to 5 days after use. More on the bioavailability, half life and detection window
They see what's already there in a different way, and most of the time, they're aware that their altered perceptions are caused by the drug. After taking LSD, the effects -- known as a  trip  -- usually start within an hour and can last up to 12 hours, with a peak about halfway through the experience.