Absolutely. While we have a guided meditation with a rhythm you can follow, it’s perfectly fine to do it in your own rhythm if your breaths are longer or shorter. For example, some people may take very short and shallow breaths. They can practice Yoga Breathing according to their own capacity, in their own rhythm. People who have been practising yoga asanas and yoga breathing may have long, slow breaths, so they can practice in the rhythm that’s comfortable for them. Even kids can practice it.
Mantra breathing can also be practised silently by focusing on the mantra as you say it in your mind. This means you can do it while commuting, when waiting for something or someone, before going to sleep, or during periods of wakefulness in the night.