Japan could've contacted America through one of the neutral embassies at any time.
They didn't surrender.
A big sticking point in the negotiations was whether or not the emperor could stay in power. We agreed to letting him stay in power, but still no surrender.
Actually, it was more than that.
It is true that Japan started to approach nations back in January 1945 in the hopes of ending the war. But they were not trying to propose a surrender, they wanted an armistice.
In essence, a return of both sides to 1941 borders. A
pro quo ante bellum. No occupation, no reparations, no demilitarization, any war crime trials would be conducted by their own government. Oh, and in negotiations they might possibly give up Taiwan, and the US would have to demilitarize the Philippines.
They tried to get 3 different Neutral nations to present that proposal to the US and other Allied Powers. First they went to the Swiss, and they refused to even consider making that proposal. They then attempted to approach Sweden, and got the exact same response. Both of those nations knew that it would be immediately rejected, and that by presenting it as a serious offer they would have lost prestige with the side they knew would eventually win the war.
Finally they went with their third option, the Soviet Union. They were their final choice, because even though nominally neutral with Japan, they were a US ally. They presented the proposal to the Soviet Ambassador to Japan, who then said he would forward it to Stalin. That he could make no promises, Stalin would have to make the final decision on where and when to present it. Of course, the Soviets were already closing in on Berlin, and were already expecting to go after Japan once Germany was wrapped up.
But along with the proposal, the Ambassador sent a note stating that he thought that Japan was insane to even propose such a thing. And that it should be rejected and never mentioned as it would affect Soviet relations with them.
And Japan after being rejected by 3 different nations never made a request for an armistice ever again, let alone a surrender. They really were that delusional, in thinking that they could dictate in early 1945 a return to 1941 borders. Including the demilitarization of US soil, as if they were actually winning. A proposal so insultingly stupid that not even the Swiss would present it for them.