The forex market is open twenty four hours a day for five days in a week if am not mistaken, as for how much to start with, it depends on the broker you make use of. Each of these brokers have their own minimum account you can use in joining, if you have more than that and you can invest it in, then go ahead. It's not a must you have to invest all that you have or a huge amount of money, though the more you invest in, gives you a better chance in the forex market but at the same time very dangerous.