There are several ways to look at this... Look in the Mission Editor and load the BattleOfMidway.mis file in the Data / Campaigns / Campaign folder, and you'll see that three of the five IJN groups are configured to start on 1942-01-01, with the scenario dated 1942-06-04. Most of the other groups start on 1942-06-04. Some might have the "EvolveFromEntryDate" status set to "true", but most are "false"... Now, use the playback feature in the upper-right of the screen, and set it to begin playing the scenario at 1942-06-01... At 0600 hours on 1942-06-04, this is what you'll get:
Battle of Midway in the Mission Editor, 0600 19420601
Looks about correct! However, the ME player started on 1942-06-01... so what happens if you started it on say 1942-01-01, like some of the groups in the mission file do? Why, those groups would start moving on whatever particular day you start the career on, if it's after 1942-01-01. If you start on December 7th, 1941, then the groups configured to run on 1941-01-01 start moving on that date. The others start on 1942-06-01. What about doing the Single (Quick) Missions version? The Singe (Quick) Missions version does NOT use the Battle of Midway.mis file in the Campaign folder - it uses its own in the Single Mission folder... That's right, the devs didn't trust their own Campaign file to run correctly... ahem (it'd be difficult to anyway)... anyway, if you're in the campaign, it will not function correctly in Stock nor most mods. What happens is that most of the groups are either long-gone, or are yet to arrive...
Besides that, even if you manage to have it "time" correctly, look at the mileage, or distance between things there. Midway is the middle little light blue smear of the three toward the bottom of the picture. Look at the kilometer scale to the left. The IJN carrier group there then is roughly 450km (or roughly 250 nautical miles) northwest of Midway. The two US carrier groups are roughly 900-100km (or about 5-600 nautical miles) north of Midway. There is about that same 450km between the IJN and the US groups. That is a LOT of ocean for a submarine to find something in, even if you have relatively accurate "intel"...
