It may not be the sexiest of workouts, but walking will get the job done if you don’t have time for anything else. Work it into your daily routine; if you’re doing laundry, carry one small stack of folded clothes at a time up and down the stair to put it away.
Working from home, and spend a lot of time on the phone? Walk the length of your house back and forth while you chat! What’s important is that you get up and move as much and as often as possible.