Would you please explain the problem in more details, in case we can find a work around for it, why do you want to increase the connection Timeout?
Instead, could increasing the CommandTimeout solve your issue?
(edit)
Also, check this out:
If the error occurred because of a slow network or system, reconfigure one or all of the parameters SQLNET.INBOUND_CONNECT_TIMEOUT, SQLNET.SEND_TIMEOUT, SQLNET.RECV_TIMEOUT in sqlnet.ora to larger values. If a malicious client is suspected, use the address in sqlnet.log to identify the source and restrict access. Note that logged addresses may not be reliable as they can be forged (e.g. in TCP/IP).
Your sqlnet.ora file can be found in your $ORACLE_HOME/network/admin directory.
ref: http://www.dba-oracle.com/t_ora_12170_tns_connect_timeout.htm
Also check this out:
http://filibeto.org/sun/lib/nonsun/oracle/10.1.0.2/B14117_01/win.101/b10117/features001.htm
And so the question can be, are you sure you need to adjust the Connection Timout or the Connection LifeTime ?