Research has shown that you can receive the benefits of meditation within 12 minutes of practise. In order to achieve this, I do a minimum of 15 minutes when I meditate…I'm speaking here of silent meditation with no guidance, however, there are guided meditations that are longer and of course they are beneficial too.
When I say yes, you can meditate too much, this is for two reasons:
Firstly, if you have an incredible, otherworldly or out of body type experience during meditation, some people can become addicted to the sensation, chasing more and more. While exciting to experience, searching for it again is the opposite of the goal of meditation – which is to accept whatever IS in the now, at all times (in life, and in meditation), and simply BE.
Secondly, if you spend an hour in meditation in the morning, great. An hour in the evening, perhaps also great… but it is worth considering if the time spent is adding to your Peace of Mind. Is 30 minutes enough? If you need 60 minutes fine, but don't do so much that it encroaches on your active life – because, as previously stated, the goal of meditation is to help you be present at all times, conscious in each moment, centred and calm. Your life should become Living Meditation, so if you feel like you're spending too much time sitting (or if you feel like you don't have enough time to sit!) bring the attention of meditation to everything that you do. Start with little tasks that you can and often do on 'autopilot' – washing your hands, waiting in line, walking through your house… Bring meditation to life.
I hope this helps!