or can I rest from time to time?
Oh, it's the tradition to practice 6 times a week. On Saturday is a day off. It's also the tradition to practice not on full moon and not on half moon days.
I guess there are more people who do not follow these rules than those who follow them.
In India I was glad for every day off. I needed it. The practices were so intensive that my body hankered for a day off. My self-practice here in Germany in a cold climate is not so intensive like in India, where I in addition practiced in a group of ambitious Ashtangis. So I interpret these rules more or less as a recommendation and not as an order.
Nevertheless: from time to time a day off or a relaxed practice is very good. After such a relaxing day it might happen that the body is even more flexible.
A daily routine facilitates to find the way to the mat day by day. The Ashtanga series are so demanding that they cry for a daily practice. Ashtanga yoga is nothing that you can do half-hearted. Either you lick blood after a while and you start loving it, then you will soon find yourself daily on a mat, or you give it up. Your heart blood must love it, then there is no way back and one day it might be that you even travel to India to the source. (my humble opinion)