1. We'll leave after lunch.
2. We'll leave in lunch.
(Can we use both preposition? Are both OK? What is the difference between them?)
3. He was dead in a few seconds.
4. He was dead after a few seconds.
(is there any difference between them? Can we use both prepositions?)
5. They will leave for London after 10 minutes.
6. They will leave for London in 10 minutes.
(Does #5 mean that they will leave for London after 10, 15, 20 minutes....? Any time after 10 minutes? Does #6 mean they will leave for London shortly after 10 minutes? What is the difference between them?)
1 & 2: 1 is find, using "after". That means after we have eaten our lunch, or after the lunch period. #2 is not correct. "In" lunch? There's a fly in my soup? What is in lunch? Too much garlic? You could say you will leave during the lunch period. It does NOT mean after lunch. It really means nothing.
3 & 4: Both mean the same thing in this instance. In both, using in and after, it means he died after the elapse of a few seconds.
5 & 6: leaving after 10 minutes could mean any time after ten minutes has elapsed. It really doesn't make much sens. #6 is correct. We will leave in ten minutes (when the train is scheduled to leave, or when the timer goes off, or for whatever reason you must wait ten minutes to leave).posted by Reed