There’s a lot of vague opinion here. Several studies have shown at as little as 20 mins (two 10 minute sittings) a day is sufficient to receive benefits. In fact this level of practice is the basis of one of the most popular book-based Mindfulness courses in the world (Mindfulness: A Practical Guide to Finding Peace in a Frantic World).
This is backed up by research conducted by Jon Kabat-Zinn and Mark Williams at the Oxford Mindfulness Centre, too.
The quality of your practice probably has more to do with benefits than the quantity.
On an anecdotal level, I’ve personally received some benefits from one 10 practice a day over a period of months, and had no benefit from several three 1 minute practices a day.
Finally, everybody can find 10 minutes in a day, even it means falling asleep 10 minutes later. 10 minutes, or even 20, may seem like an impossible amount of time to find, but one of the first things you learn, when you force yourself to make time to practice, is how much time you have to spare without realising it. Really. You’ll be amazed.