Hello, Claire, and welcome.
I think you'll get a variety of answers on how often and how long. For me, what is important is to do it every single day. Depending on my work/life schedule, I might only be able to sit for 10 or 15 minutes each morning, and at other times I'll sit for a half hour or longer and sometimes more than once a day. So the length of each session fluctuates a lot, but the "daily" part stays constant.
"To reach beyond fear and danger we must sharpen and widen our vision. We have to pierce through the deceptions that lull us into a comfortable complacency, to take a straight look down into the depths of our existence, without turning away uneasily or running after distractions." -- Bhikkhu Bodhi
"No man ever steps in the same river twice, for it's not the same river and he's not the same man." -- Heraclitus