Seller has not contacted yet. How long should I wait...

I have to agree with what bdp24 said. You can't expect a seller to be as fast as Amazon. People have other priorities in life. I can't believe that due to the OP not hearing back from a seller in 12 hours you are ready to escalate. If it isn't a pro seller I'll give the person 2 business days before I inquire. If it is a pro seller I'll give them 1 business day.

Please do not get me wrong. I was not trying to "escalate" the issue. I was just curious about how long you guys normally wait before becoming concerned.

I fully realize he has a life. We all do.

I recently  sold a unit that buyer had no feedback  and never communicate. 
Audiogone hold my funds on express checkout for 8 days after item was delivered since buyer did never said a word. 
Fortunately  happy ending I got my funds. 

A few weeks ago I did a Buy it Now, and the Audiogon system instructed me to wait for an invoice from the seller before making payment. When I didn't hear from him for a few days, I emailed telling him about Audiogons message to me, and asked for a total with shipping. Heard nothing for a few more days, but did eventually. I made payment, heard nothing about my payment having been received, but did get a tracking number and a thank you. Not how I do things, but I was raised right ;-). 

... and we have contact!