The setup routines, including setting the clock, must be completed before a Magnavox 515 can be operated. If you set the clock to automatic and there is no channel feeding a good time signal to the internal tuners there will be operational problems (including a channel and time search just before noon and midnight every day). Set the clock manually and set auto clock to OFF.
Your situation is described in this AVS Forum post:
My new 515 was set up for the first time today. This 515 is one of my eight Magnavox and Philips HDD/DVD recorders.
The first post in Wajo's sticky thread is the gateway to a wealth of information concerning the Magnavox 515 and earlier models:
That very active thread now has 12,604 posts viewed 1,193,358 times.