This question already has an answer here:
I am newbie for scrum. Lets say we have all the user stories for the product, and the product owner gave them the priorities. Now as a team, when we should estimate times for these stories? Should we estimate times for all the stories roughly before the sprint planning then updating them if it is necessary during sprint planning?
Actually I am curious which part of scrum first time estimation should be begin? During sprint planning or where?