There is an active discussion on the benefits of using either story points or hours for sprint planning. This discussion is devided up into two camps, and each have its own set of reasons of taking one approach over the other. Here are some articles on the topic:
When talking about this with our customers and following the discussion online we've found that it is quite common to use story points or "t-shirt size" (relative sizes) in the planning or estimation phase for ranking the product backlog. Then, when the work starts you break down the requirements into tasks, and when this is done you switch over to using hours instead of using points.
In VisionFlow there is good support for managing hours per story/task which is the most common way to manage time and task size on tasks in the sprint by our customers.
To use t-shirt size on epics/stories you need to add a custom field for this. You can do this in General --> Settings --> Issue configuration --> Custom fields.
To use "Story points": Its a standard field but is not used by default, so go to General -> Settings -> Issue fields, and select the issue(task/story) field configuration to use, and add the "Story points" field. Now, when in a project that uses this field, you will get the option to see burn-down graphs etc calculated on story points as well.
(Note: Support for story points were added in v7.3)