Grinding and leveling for the sake of it? Rather not.
Side quests? If they are well made and the game is engaging enough, Yes please!
So I guess it would be just around 50h for my play style...
I spent around 82 hours on the game. Didn't do any grinding except in chapter 5, where I grinded for maybe 2 hours when I completely revamped my party, and that was good enough for the rest of the game. I played on Hard mode btw.
I did do all the sidequests, even in chapter 5 and 6, and beat all the optional bosses I could (including Nemeses in Norende).
By chapter 5, after I finished my grinding I avoided most random battles, which would've added more time to my playthrough. And 82 hours isn't counting deaths. Some bosses I had to spend more time on than others.
The game is pretty lengthy. FE probably has more meat to it, but it's also far more grindy. I couldn't even stomach FE for more than 30 hours.