I didn't rush it and did a full play through as Ravensclaw and Slytherin, plus the other two houses to get the house specific missions for the achievement.
Press the Xbox button to open the guide, then select Game activity > All achievements.
Select a game, then select Stats.
On the web, see your time played:
Sign in at account.xbox.com.
Select your gamerpic (top-right), then select Xbox Profile > Achievements.
Select a game, then select Achievements again. You’ll see your minutes played among the stats shown.
For a totalthere might be some site or service that helps with that but I don't know of it.
Edit: actually Xbox is doing a year in review right now that has the total.