You can reserve a bike from the mobile app for up to 10 minutes, so it will be waiting for you when you arrive.
Please note that the amount of time a bike is on reserve for you counts toward your total ride time. If you're a Pay As You Go plan member and reserve a bike, but aren't able to pick up the bike by the time the 10 minute reservation expires, you will still be charged the $.08/ per minute.
To reserve a bike, click on a station icon or a single bike icon on the map, then press the button that says “Reserve a bike at this hub” (or “Reserve this bike” for single bikes not at a station). If you change your mind, you’ll have one minute to cancel the reservation without the time counting against your account or without facing a $.08/per minute charge as a Pay As You Go member. When you arrive at the bike you've reserved simply enter your PIN, unlock and ride!