Attack Ideally in May or June, that gives you the whole summer to neuter the Soviets as much as possible because you cannot compete with the Soviets when it comes to manpower and battles of attrition and the huge combined IC of the USSR, USA and the UK. Also it depends on where you attack, do not attack into what was formerly eastern Poland, it is swamps and forests which are slower to move through for your Panzers, I would advise getting Romania on your side, then attack in your southern border with the Soviets from ah Chelm I believe the province is called, concentrate your tanks there, keep infantry along the northern border to hold the provinces. A strategy for invasion I find useful is to drive my tanks to towards Odessa but instead of going straight to Odessa I travel along the usually undefended provinces that are east of the river of Odessa, thus putting a river between me and the Soviets should they try a break out with infantry pushing down from the north and the Romanians to the west of this southern pocket. For the second part of the strategy, I have my tanks drive north towards Kiev, avoiding actually fighting in Kiev because that would be an urban battle and quite a bit ahead of your infantry, avoid battles as they slow you down having to fight the actual battle and then the reorganisation time after that where they can't move, time is precious in the summer months. I then push along the eastern side of the river running north and south by Kiev, thus putting another river on my side should the Soviets in the pocket I am creating attempt to break out, then driving north to Smolensk and from there they turn west towards Riga, spreading out my armoured forces along the provinces I have created a large pocket trapping a good size force of the Soviet army. Once you declare war on the Soviets what I find helpful is to logistical bomb the provinces of Eastern Poland where the Soviets have quite a few big stacks of units, this will slow down their movement through the swamps etc. and stop them from rushing to break out of pocket. Also Divisions pushing north into the Baltic states from Klapeida to link up with my tanks at Riga to speed up the encirclement. Don't try and take too much at once with the Soviets, they are magicians are producing divisions from thin air, i.e. redeploying their far eastern divisions to suddenly threaten your front line unguarded provinces. Then your infantry along the centre border now attacks across the river into the swamps pushing the Soviet units one province at a time.