Release and iteration planning are important activities in the Scrum process. This is related to Release and Deployment Management process identified by ITIL.
During release planning we do not split user stories into engineering tasks. That part is done in iteration planning.
Here we define which user stories will be delivered in the release and how long it is going to last.
User Stories are broken down into tasks for each iteration. The tasks are then estimated in hours.
Reference: Agile Estimating and Planning, Iteration Planning, page 152.
Task estimates are expressed in ideal time.
Reference: page 156.
The Right Size for a Task
The average size of tasks should be such that a developer is able to finish an average of one per day.
Relationship between task estimates used during iteration planning and the story points or ideal days used for longer-range release planning.