The joy of meditation and of a meditation practice is that you get to choose. You can meditate for three seconds, three minutes, or three hours. I would recommend all! We meditate for many reasons - to take a pause in a heated moment (three seconds and tuning into the breath is a cracker for this!), or we take three minutes to bring some calm, to re-centre, or to transition from one activity to another. Or to deepen our practice and to bring a depth of awareness to our selves and our lives, we practice for longer - it's amazing where three hours can go and what richness that use of time can give you.
It's really up to you how and when you practice, but to feel the benefits we know from research that a regular and committed practice of between 10-40 minutes a day is ideal.
We do not learn to run by sitting on the sofa eating peanuts and drinking a chai latte, the same goes with a mindfulness and meditation practice. You can take it with you too, practice as a passenger on a bus, sitting on your front doorstep listening to the world, tuning into sounds in the workplace, or just before you turn in for the night.
Have fun with it, experiment with whatever works and supports you, but do make it a habit. It's where the magic happens.