This has been covered ad nauseam in the past. Feel free to search the post history for links to the actual forms and applicable laws.
A Reit has until they file their tax return to distribute cash and have it count as a distribution of prior year earnings. That makes complete sense when you think about it - most companies do not know how much taxable income they will actually show on their return at 12/31, so expecting a REIT to know exactly what 90% of that number would be ridiculous.
As you pointed out, they can file a six month extension in March, so they don't have to file their actual tax return until September. Effectively giving them until September of the following year to distribute enough cash to cover the prior year's earnings. Its just kicking the can down the road.
YBF, have you looked at the 10Q?
Last time I looked there seemed to be some kind of clause or something about taxes that lets them get out of distributing it.
Or something about avoiding getting a heavy tax penalty on it if they don't distribute it in time.