If you take omeprazole at night, and it has to be on empty stomach, how long after eating show you wait to take it? It lasts 24 hours?

Acid Awareness. Omeprazole, like other proton pump inhibitors which reduce acid production, is advised to be taken on an empty stomach. This is to improve absorption by the body during a time when acid secretion is actually not desired, i.e. Sleep. Taking it 90 to 150 minutes after a large or fatty meal would be ideal. Eating within three hours of bedtime is never advisable on acid suppression therapy.
Omeprazole. Ideally you should take Omeprazole before meals in the morning, and same applies to in the evening, but if you want to take after meal I would recommend wait three hours after meal, but if you have to go to bed before you can take at bed tim, it will still work.