'Certain days in the month are considered “anadhyayana” days. Some
people ask if Yoga should not be done on these anadhyayana days.
During my studies with my teacher he did not specify any days when we
should not practice Yoga. Anadhyayana is usually associated with study
of the vedas and anadhyayana days are days one should not study the
vedas, presumably with the teacher. In short we may say that the veda
pathasala or veda schools would be closed on these days. I started
learning veda chanting (with my father) when I was about 10 years old
and I had a teacher who would come to our house at about 5 in the
morning to teach vedic chanting. But he would not come on these
“anadhyayana” days. The smritis say that vedas should be chanted daily
(vedam nityam adhiyetaam). So we may say that the prohibition is with
respect to studying, perhaps new lessons but not chanting the portions
already learned (swadhyaya). On anadhyayana days like the new moon
day, one may refrain from learning with a teacher new vedic lessons,
but may chant what one has already learnt. It is a moot question if
this restriction applies to yogasana learning and certainly does not
appear to apply to home yogasana practice.'
I guess this means it's a seven day a week practice too. I think someone said in one of the interviews in GURUJI that Ashtanga used to be seven days a week practice, 'back in the day'. Never liked taking a day off anyway, would feel fidgety and restless all day and end up doing an evening practice of sorts when I got home from work. Of course with VK you can regulate your practice a little more, perhaps a lighter or shorter asana practice once a week allowing you to spend longer on your pranayama and meditation practice.