All currencies trade 24/7 (if they are traded).

The volatility has quite a few causes, among them:

- Other currencies are used for all sorts of things that don't involve trading them–i.e. when have you last thought about exchanging those USD in your pocket for Euro? That creates stability. Compare to bitcoin, where almost everyone owning any keeps an eye on the market and is principally willing to buy or sell when they think they see an opportunity.

- Markets for real currencies operate under government supervision and regulation, and the facts that influence their value, such as employment numbers or GDP growth, are public, and reliable. For bitcoin, some rumour from China can move the market because nobody knows which information to trust.