For or During

For + time is used to say how long something was done.
During + noun is used to say when something was done.

  • I was reading for the whole of yesterday.
    (how long/all yesterday)
  • I was reading a lot during my holiday.
    (when something was done/holiday)
  • We have been waiting for two hours for him to catch some fish.
  • During my shower, I had a great idea.