Your numbers are a bit dodgy there! It takes the same amount of time to say Asr as it does for Isha and Zuhr?! Isha is only 5 minutes longer than Maghrib? And only 8 minutes for all the wudhu you do in the day?!
Anyway, very good point you made!
I dunno, I was going based on past experience. I was being a bit generous actually because I used to time this stuff and it took around 35 minutes to get to the mosque, wait for the prayer to start, do the prayer, sit down for about a minute (I don't know why people do that), find my slippers, and then go back home. And sometimes it would be 20 minutes to go til Isha when I got back from maghrib prayers. Ridiculous LOL.