This is the reason I'm single. I don't have patience for useless arguments like this. You commute whatever amount makes you comfortable. If you do it more and hate it because it's more than you're ready for, doesn't that miss the whole point? How many days a week does your wife commute by bike? You didn't mention that she does, so I'm guessing 0.
I think she's just looking to pick a fight, I'd stay at the pub for a couple days until that passes. Seriously, you're not going to win this one, do your best to keep it from getting bigger than it should be.
Ask her to be happy that you have some outlet and see if she wouldn't mind letting you manage your own time with it. It's absurd for her to try to dictate what she, or any other forum member here feels is appropriate for you. Good luck.