I was working on a new work item template (WIT) for Team Foundation Server 2010 and I encountered a requirement for a datetime field where the user could select a the date and the time a specific activity was done. The DateTimeControl for TFS work items displays only a date picker by default, which for this particular use case was not quite accurate enough.
Searching over the web I’ve found a good post of Nick Hoggard in order to do this.
Simply, you have to set the Format and CustomFormat attribute of the control in the work item definition. That’s all!