The expiry time is the point at which a trade is closed and settled. The only exception is where a ‘Touch’ option has hit a preset level prior to expiry. The expiry for any given trade can range from 30 seconds, up to a year. While binaries initially started with very short expiries, demand has ensured there is now a broad range of expiry times available. Some brokers even give traders the flexibility to set their own specific expiry time.
Hello, I was reading some blogs that are helpful, I think that trading on binary option is about a good strategy. But also I think we have to look for a good broker. I use a signals service which I think is very good, they send me signals every day and I don’t have to pay for them, also I use a broker they recommend stockpair, I made a research before I started and I think I am doing it good (I wish It could be perfect LOL)
Nadex binary options don't have rebates on losing trades, but if you buy an option at 50, and it drops to 30, you can sell it for a partial loss, instead of waiting for it to drop to 0 (or move above 50, which would produce a profit). Ultimately though, at expiry, the Nadex option will be worth 100 or 0. Therefore, when determining your risk you must assume the worst case scenario. 
A binary option is a financial exotic option in which the payoff is either some fixed monetary amount or nothing at all.[1][2] The two main types of binary options are the cash-or-nothing binary option and the asset-or-nothing binary option. The former pays some fixed amount of cash if the option expires in-the-money while the latter pays the value of the underlying security. They are also called all-or-nothing options, digital options (more common in forex/interest rate markets), and fixed return options (FROs) (on the American Stock Exchange).[3]