I'm unsure. I'm aiming for 3, once in the morning, once in the afternoon when I'm feeling my most stressed and disillusioned and once in the evening before bed after "unplugging and disconnecting".
That depends on your current practice. It is hard to rest and clear our mind if we are not used to it, so for starters once a day is enough for five minutes or so. Once you can clear your mind and focus on your breath, it will become easier to contemplate your object of meditation. Do this until you feel comfortable with it, without your mind running around and distracting you, and then it is just a case of increasing the number of times you meditate per day/week and the length of it. Do it at your own pace as you are the only one that can control your mind.