Normally 30 seconds would be more than enough, and often a lot less such that all the lights are normally stable.
If you are getting a connection between the modem direct wired to the PC, that suggests your PC and that cable are correct. If you simply unplug that ethernet cable from the modem, and plug it into the router LAN and boot the router, you should now get an IP from the router, and be able to brwose to the router's admin pages. If that isn't happening then maybe something is broke on the router
