The amount of Resources you can get from each Stronghold is limited - 50 000 Resources a week. It includes Resources gained from Raids and as Gifts via the Galleys.
You can go back and raid the Stronghold again in 7 days.
Another important thing to remember is that the basic number of Raid attempts is limited as well - maximum 10 attempts. You get new Raid attempts every 2.5 hours.