Good question! It doesn't say on the website, unfortunately. At my dojo we do a similar set of exercises before training (so 3 times a week). I don't think the exercises in the article are too strenuous so you could probably do them more often.
Thanks for noting the weird layout. I initially thought there were only three exercises. I've been enjoying the pigeon pose and 90-90s for hips. I need more shoulder flexibility exercises.