What if D Day was delayed for a month and the Bomb was ready 6 months earlier?
Twin PODs for this, the first is plausible but the second is close to ASB
1) Ike doesn't risk the invasion of Europe on the strength of a weather forecast, but instead decides to postpone until the next period that the moon and tides are right
2) Here's the tricky one: EVERYTHING goes right for the Manhattan Project.
No bureaucratic or diplomatic squabbling, no holdups in building the facility or delivering materials. No time spent following scientific or engineering dead ends; every experiment and test goes right first time.
There are no delays of any kind (trivial examples - there is always a sharpened pencil when it is needed, typewriter ribbons don't jam while a report is being written) and there are no accidents, injuries or fatalities.
In other words Murphy's Law has been repealed.
For arguments sake lets say that the Trinity test takes place exactly 6 months before OTL VE Day.
So what happens?
Does a delayed invasion help the Germans, giving them more time to strengthen the defenses? Or favoring the Allies because recuperating units have returned to the Eastern Front?
How far West do the Soviets get?
What is the first city to disappear under a mushroom cloud? Would a second bomb be needed?
What is the reaction of the Japanese? How do Germany's other allies respond?