guide data update

We use our Tivo OTA in our rv and have it connected to the internet through a router. At bed time we turn it off the router. I was told that every 2 weeks at a minimum I need to let it stay on to allow for the update to happen. How do I find out what night I need to do this? What time? And then is it every 2 weeks after that? Is there a way to do it manually?

thanks in advance for your help