I was asked how often would be good to do zen meditation?
Well, you eat about three times a day and you brush your teeth afterwards every time. And, every time you skip it, tiny scraps of food stick between your teeth and are either noticed by your partner or by bacteria. This how you learn to brush your teeth regularly to keep them healthy.
But, your mind is fed every moment with things you read, hear, see, say or think. Why do you think that it is not necessary to purify your mind regularly too or that cleaning from time to time may be sufficient?
When you get aware of this simple principle, the answer appears too.