When should Germany have surrendered?

[Grumbler]

February-March, 1942. That would have satisfied the treaty requirements with Japan and left them isolated.
Remember Hitler made several overtures toward negoiating a peace with the Allies. He was NEVER going to surrender, but he had acomplished most of his war goals as laid out in Mein Kampf by spring of '41. There is no way to know how 'offical' Hess's trip was. Keep in mind that a considerable portion of the UK wanted peace. Churchill was keeping the war going by sheer will on his part.
Churchill knew that the only chance of survival the UK had was America. Only America had the industrial capacity and manpower to save England.
The Anti-war movement in the USA was many times stronger in '41 then it is today or was during Vietnam. FDR was re-elected on a pledge of not going to war.
Germany declared war on the USA on December 08, 1941.
If they hadn't FDR WOULD NOT have gotten Congress to declare war on Germany. The 1940 census had 40+% of American identifing themselves as being germanic. Germany was greatly respected and well thought of. Hitler was admired as a strong and energetic leader. Read some of the press of the time.
If Germany hadn't declared war on the USA, we would NOT have gone to war against Germany. Churchill would have had to give up his crusade. If Germany had allowed England to keep Egypt, It's likely that the British would have gone for that sort of deal, not having the USA to fall back on. Hitler would have had his revenge for WW1 and 'living room' in Poland. Eventually Hitler would have attacked the Soviets, if they didn't attack him first. Stalin claimed a lot of things, but the facts are that he had his armies deployed in offensive positions, which is a big part of the reason the germans went thru them so fast in the summer of '41.
If Hitler had offerred to negoiate a deal with an England standing alone in Europe and getting an ass wooopin in Asia and N. Africia, I suspect the Brits would have made the best of a bad deal and taken it. It would have been foolish to do anything else.