SBG8300 parental control issue

First, understand I am not tech savvy.

I have an SBG8300 and it won't let me add, edit, or delete words or sites in the parental control area. I have 18 blocked sites and 26 blocked words entered. Is there a limit?  If so, how do I delete when it won't let me? I'd reset the SBG8300, but I'm afraid I will not be able to reconnect with all the correct settings for xfinity connection (this is where the tech savvy part scares me).

Also, unrelated to above, I have a 2.4 and a 5 GHz wifi set up.  They work fine, but can I set one of them to turn OFF at night?  I need one one for security cameras, but want the TV and phone shut OFF at night so kids will sleep.