There's a reason why double-planting soybeans after wheat is more common in southern Indiana, or at the least the southern half to two-thirds of the state. In most years there isn't enough time left after wheat harvest until the first frost for soybeans planted in northern Indiana.
Shaun Casteel, Purdue University Extension soybean specialist, hopes that doesn't come into play for those still trying to plant or replant first-crop soybeans in slews and wet areas within the field this year.
If you do have to plant in later June, he recommends upping the seeding rate dramatically, going to narrower rows than 30 inches if at all possible, and from this time forward, moving up half a maturity group. If you would plant a 3.5 maturity group in your area for a full-season soybean, then switch to a 3.0 soybean or as close to that as you can find for this late in the season.
Casteel usually suggests checking the fall freeze date in your area. Then go back 90 days. If you can't plant by that back-dated date, you may not have enough time left in your region to mature a soybean crop.
Note there is a difference between first frost and first freeze days. Say the first Freeze sate in your area is October 15. Then if you go back 90 days you're roughly at July 15 as the last possible planting date.
Depending on the season, there's no guarantee that the crop will mature before a freeze shuts it down. The current 90-day forecast through August form the National Weather Service calls for normal temperatures. That translates into an equal chance of below normal and above normal temperatures for the period. In the extreme northern counties, the summer may average cooler-than-normal.
The latest I personally know of someone planting soybeans after a sudangrass crop was chopped off is July 17 in 30-inch rows in regular tillage. The soybeans matured, and made about 33 bushels per acre. It was an older variety. That wouldn't happen every year, and is truly weather dependent.