There is no set timeout, it depends on the OS in use and network setup.
For example if the IP address you are looking is not accessible, the routers/interface may return quickly. It could also be that a firewall is actively refusing connections thus the error will return almost immediately. The longest timeout is generally if the machine is reachable but nothing is listening on the port you are connecting to.
Generally the longest timeout on Linux and Windows is around 20 seconds, but again that can vary with the OS and I believe ALL OS'es do have a eventual timeout and its normally well under a minute.
When in doubt we always suggest putting a TIM= on the OPEN and ALL TCP communications.