TS, I had similar problem too where exercise is usually skipped due to workload and timing and because of it, I had reduced my workout plan to push-up and sit-up. It sure help to maintain the body shape but just bear in mind that you wil be doing similar workout everyday and you will be tempted to want to try out other kind of workout, hence putting a stop to the push-up and sit-up. Just keep focus on these two simple workout and it will help out with the body shape.
Merry Christmas Y'all!