Flat tire keeps occurring while bike is stationary. MYSTERY I keep changing my tube. It get's a hole right near the base of the valve. I've checked the rim, there's nothing sharp. there's nothing sharp in the tire (the hole's on the inside anyhow). and it always happens while just sitting in my garage not while riding and bumping into rocks or such. all of a sudden from what I cannot determine you hear a hissing sound as air starts escaping. The tube was pumped with ~75 psi about 2 weeks ago, and the tire says max 80, min 50. the rim tape is intact.

Please suggest what could be causing these flat tires, why is there a delay from when I stop riding it and 8 hours later between getting a flat.
I had a similar problem on my bike. The manufacturer had made the rims too deep and it was causing the tube to conform to the odd extra "U" shape when pumped up. It took a while to figure out why I was going through so many tubes. 

Check with your manufacturer / retailer. I got mine replaced free of charge.

Perhaps your rims have an abnormality near the valve hole.