This question leads on from the comments on this post

What is the minimum amount of time that one could productively sit in meditation? For instance if I only had five minutes to sit should I do it or would the time be so short that I should just not delude myself with the pretense of a 5 minute meditation. What about 10 minutes does this change it? Or the other extreme could I sit for a minute - would it be worth it?

I would be interested if anyone could give references from established teachers past or present on recommended guidelines, practices around this.