I just ran this last week. To anyone using ONX to follow the route, whoever logged the trail into Onx logged it wrong in several places(took highway when its supposed to be on trail, wrong trails altogether especially near copper harbor.) If you follow Onx route, you will hit a locked gate near copper harbor(because it has you on the wrong trail) I marked it on the app as a closed gate.
Other than that, I dont see any way that anyone could do this in 7 hours unless you are doing 60mph most of the time.(most of the way you will find that 30mph is more suitable depending on your vehicle)
I spent about 10 hours before bailing onto US41 to make some miles and catch sunset over the lake.(then I caught the rest of the trail the next morning)
The only challenge I ever hit was near the WI/MI border, the trail got tight, rutted, and there were several fairly deep mud holes. I was in a Stock JKU on this trip instead of my normal rig, the water was deep enough that it came close to bottom of doors and exhaust was bubbling underwater but I made it.
One of the final sections out near rocket range has lots of water holes with firm bottom, they were all passable (for reference a suburu was following me) but some of them have the potential to be 4-5 feet deep or more if there is enough rain/melt to fill them all the way. All in all this was a very fun adventure. Being from the midwest I had no idea that we had a route like this even remotely close.
You can get fuel in Sidnaw but it was $5.69 per gallon 91 octane 0 ethanol. (for reference everywhere else the normal cheap gas was $3.69) they didnt have normal pump gas but she said 6 miles up the road there was