Got 5 -10 minutes? Take a Qi break.
Got 20 minutes? Get your Qi flow on.
Got an hour - you hero. See you out there Qigong-ing it up.
Really it doesn't matter how much time you have, any Qigong is better than no Qigong. You will immediately feel the benefits even if it's only a quick 5 minutes squeezed into your break time.
Advice on how often you should practice Qigong is varied, with some experts recommending 20 minutes 3 times a week, others recommend an hour a day personal practice followed up by another session where you learn new techniques and do your Qi homework. Really what matters is that you listen to your own body, you will know the right balance for your lifestyle.
You might just find that you don't have time not to do Qigong.