How quickly will I see results using a rowing machine?

I've decided I need to slim down/tone up for the Summer holidays, but mostly just tone my body. A daily intake for me would be all-bran flakes with skim milk and strawberries for breakfast, a salad for lunch, and a bowl of rice with peas for dinner. Sometimes I snack on fruit/nuts/veg during the day. I've decided I want to be using a rowing machine for 20min four days a week. I also run 2.5km and walk 2.5km every other day. How quickly will I see results?