Anytime I try to modify an address through MM, if it does eventually get confirmed it takes weeks. I've had better luck requesting ownership through support even with waiting the full 7 days and then changing the address from the dashboard.
As Joy pointed out last December, it's technically against map maker terms of service to change a location's address in map maker, though it's not against TOS to make that chnge in the dashboard of an owned GMB account. I've seen a lot of spammers try to get under the radar by changing one company's information to their own company's information, so you can see why it's not good for Google to let people play too fast and loose with NAP info on unclaimed listings.
The main place I see this coming up and causing problems is for businesses that moved, but never claimed their account and now can't receive a verification postcard at the old address. Stuff like that's a pain, though as Colan and Heckler pointed out, regardless of rules it's still often possible to get the address changed through map maker if you're patient. Still better to try and claim it and change in the dashboard instead though if you can.
Either way though, if you own the listing I can't think of any reason why you'd ever make a change in map maker instead of through the listing dashboard.
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