How long it takes to recharge and how often it has to be recharged?

You recharge as needed. From very low to 100% should take around 3 hours. I can take my Watch off charge at around 7am and use until just before midnight, and I still have a little under 50% battery left, and I consider myself a rather heavy user, with work and personal mail, messages, Twitter. And my work mail is an Exchange account that uses Push. With light usage, it can last almost 2 days.