You have some flexibility, Young Grasshopper, but not much. Let’s say you try a January 1, 1943 start date.
At that point, the Americans had already gained naval dominance in the Pacific at the Battle of Midway back in the summer of 1942, and the Americans were massively outproducing the Japanese all through the summer and fall of 1942, so the Imperial Japanese Navy is going to be outnumbered roughly 2:1 vs. the US Pacific Fleet if you want any kind of historical realism. What the Japanese still had going for them was control of a middle and inner layer of defensive islands – you could give Japan some infantry and some land-based fighters on Iwo Jima, the Mariana Islands, Palau, and New Guinea, and you could leave the American transports back in Hawaii or even San Francisco, to show the difficulty in transporting troops over the entire Pacific Ocean.
In Africa, the Allies have seized Morocco, Algeria, and Libya. You can leave Tunisia in German hands, but it wasn’t held very strongly – it’s not really a useful beachhead; the Germans couldn’t afford to reinforce it, much less counterattack, without dangerously draining forces needed to occupy France or occupy the Balkans. Even if you leave the Germans in Tunisia, with American, British, and French forces all converging on Tunis, it’s only a matter of time until Germany gets pushed out of Africa.
On the eastern front, the Germans were crushed at the battle of Stalingrad, but they still held Rostov and the Caucuses in force, which makes for an interesting opportunity for the Germans to push forward. In real life, the Germans sensibly retreated from the Caucuses, but they could have doubled down with their last remaining reserves on the eastern front to try for Round 2 in Stalingrad, or to try to break into Persia and Iraq. The German front line at the time would have been something like Baltics - Belarus - Bryansk - Rostov - Caucuses. It’s a good front line, but the Russians are mustering a very large counterattack that will almost certainly break that line. The Germans could plausibly take Leningrad, Stalingrad, and maybe even Persia, but even if all of those battles went well, they would not have any realistic opportunities for breaking through to Moscow for at least another 4-6 turns, by which point the Allies are almost certainly sitting in Paris and Rome and threatening Warsaw.
The Japanese could plausibly have crushed the Chinese resistance in 1943 if they had poured additional tanks into the region instead of reinforcing their barrier island chains; it’s unclear if that would have had any serious effect on the defense of Moscow. As accurately reflected on the 1940 Pacific map, Moscow is 7 turns away from the Japanese industrial complexes on the eastern coast of china – even if China were totally undefended, it’s hard for Japan to move significant forces all the way through China and into Russia.
So, long story short, I think you could make an interesting game out of a January 1, 1943 starting setup, but you would need different victory conditions to give the Axis a chance at winning – maybe an economic victory condition, like the Axis win if they control 100 IPCs (I have no idea of the proper number), or something like that. The Axis could have made some major economic gains against the allies if they had a good year in 19432, but they just aren’t in a position to realistically assault more than a couple of victory cities in January 1, 1943, let alone in a position to conquer any Allied capitals.
