The allocations have to occur within the period of time from the passage of interim supply--therefore it can't be before the beginning of April--to the end of June. Then the allocations are provided to departments in the same way that supplementary estimates are provided to departments. They're able to spend once they receive the funds. So they could receive the funds any time from the beginning of April to the end of June, depending on whether they passed all the tests.
On March 5th, 2009. See this statement in context.