A good question, lets assume he did have these atomics then.

These are the big five

Moscow, and the delivery system would be one of the Me-264 Porototypes and that aircraft would be guarded by every available fight/Fighter/Bomber he had left in the east.

London, again by another Me-264 prototype and would be shielded by every aircraft in the west.

Washington DC, the third prototype Me-264 would be use on a one way mission

New York, this could be acieved by a suicide crew manning a U-Boat.

Paris, By a modified Bv-222.

With the total annialation of Moscow and the complete loss of the entire political and military leadership the Soviet war machine falls apart, Hitler threatens to level Leningrad if the Soviets don't unconditionally surrender, they have no choice.

London being the centre of the Government and the Royal Family and the heart of Britain and with it's destruction Hitler threatens to wipe out the Industrial Heartland of the Midlands, i believe that with the threat of another atomic Britain would be forced into uncondidtional surrender.

Paris, Hitler would threaten to use one on Paris and knowing the French they would again surrender, they would have no choice.

Washington DC, The political heart of the US.

New York, the financial capital of the world, enough said and the heartland of the international Jewery.

If this was able to buy Hitler enough time say three months as original post suggests then if the US was still in the hunt i have two more targets

Chicago, Illinois USA, the industrial heart of America.

Richmond, Virginia USA the largest naval base in the Atlantic.