If the mind is light and the energy is good, it is okay; not if, as you sit longer, the mind becomes weaker and weaker, and drowsiness comes. I also don’t encourage yogis to sit for too long because I want them to bring the awareness to other activities besides sitting.
Also, they may be attached to sitting. But we are not trying to get rid of the sitting; we try to get rid of the attachment to sitting.
It depends on the situation. Check your quality of mind while sitting – if it is awake and alert, sitting the whole day isn’t a problem.