The line port is used to connect an incoming service, such as a landline, magic jack, nettalk etc. Only the Obi110 has this.
The phone port is the one you would connect to one of your existing phone jacks, which would provide service from the Obi to all jacks connected to that wiring. (Make sure there is no other active service on the wiring efore you connect the Obi to it). Instead of plugging your phone into the Obi, you plug it into the wiring and then plug your phone into the existing wiring. All Obi devices have this of course.
The Obi has a do not disturb feature, but it must be activated using a star code every day also.
Google voice has custom ring schedules that you can set for each individual forwarding phone in your list. At your google voice phones list,
select "Edit" for the phone you wish to set a schedule for
select "show advanced settings" (this step not required for your Google Chat phone)
select "use custom schedule" for the ring schedule settings
You can set the multiple time ranges for weekdays and for weekends.