ConnectTimeout is an Integer property that indicates the number of milliseconds to wait for successful completion of a connection attempt for the IOHandler. 

The default value for ConnectTimeout is 0, and indicates that the default timeout value for the protocol stack implementation should be used when establishing the client connection. 

ConnectTimeout is not used in TIdIOHandler, but is provided for compatibility purposes. ConnectTimeout allows a client using a socket-based IOHandler, like TIdIOHandlerStack, to access the protocol stack to set the timeout value. 

Use the ConnectTimeout property in the TIdTCPClient to set the connection timeout without specific access to an IOHandler. 

Use ReadTimeout to indicate the timeout value when reading data from the IOHandler. 

Applications do not normally assign values directly to the ReadTimeout or ConnectTimeout properties in an IOHandler. Assign values to the corresponding properties in TIdTCPClient or a descendant class.

ReadTimeout 

TIdIOHandlerStack 

TIdTCPClient