The default DHCP timeout is nearly 30 seconds on most Gentoo Linux systems. This can be a frustrating on startup if you already have wireless connected but are forced to wait on an unused ethernet interface. On most networks the DHCP timeout can be safely lowered without problems.
DHCP can be provided by many different modules, but I am assuming that you have the dhcpcd client installed for this example.
To change the timeout you need to add the following line to the networking configuration file located at /etc/conf.d/net.
dhcpcd_eth0="-t 3"
This line will set the DHCP timeout to 3 seconds for the ‘eth0‘ interface.