Hello Mr. Bacon Lettuce Tomato Sandwich.
If your signal was dropping off at night, I would suspect your LNB is "temperature drifting". This is caused when the local oscillator in your low noise block is affected by temperature changes.
However since it comes back on in about 30 minutes, then we can rule this out.
Next up..a microwave signal can "drown out" the signal, this is called terrestrial interference.
Since you live on the "fringe area" of the spot beam, this makes it even more suspect.
Since your conus satellite transponders would come in strong, the TI would not be enough to drown it out, but since you live on the fringe of a spotbeam it would be easier for this to occur.
There are MANY things that use microwaves, such as airport radars, military radars, weather radars, etc. I don't know much about what frequency bands they use.
Thing is, most transmitters are not allowed to operate in the Ku band (I think), but one that "leaks", or broadcasts too wide on the spectrum, could cause interference.
Get on Google maps or Google Earth, and look in a line of direction similar to what your dish points.
If your near a military base, airport, or weather radar, this can be the source.
If you can pinpoint the place it's coming from...I would kindly call them and explain one of your radars is causing interference with your dish reception. Like I said before, I don't think airports and what not are allowed to interfere with Ku satellite reception, but I could be wrong.