Don't think about it as just a way to "speed up" your weight loss. If you're tired when you get home now, start your walking (or any of the other workout suggestions above) and you'll be shocked at how much energy you have after only a week or so. It seems like you'll be more worn out, but it will actually have the opposite effect. And, in my experience, exercise begets exercise. The more you do it, the more you'll want to.
Do it now. Don't tell yourself you'll do it tomorrow or next week or next month. Just like making the decision to lose the weight, you have to make the decision to get fitter, not just thinner. Adding the exercise will help you burn the right kind of weight off, and you'll not only lose faster, but you'll lose more where you want it from.
Go. Walk. (or run. or swim. or dance. or wrestle with your kids. or ski. or...)
"The grass ain't greener, the wine ain't sweeter, either side of the hill" The Grateful Dead