It depends on a few things, but usually 3-4 months. Standard 2 hour callout. You can be assigned ready reserve (airport standby, hot standby, whatever you wanna call it) as well. Stand-alone shifts are 8 hours at the airport. 20 minute call out.
Ready reserve is only a temporary agreement between the company and SAPA. It'll go away as soon as the 2002 Olympics in Salt Lake are over...they promise.