Yes: total BTC miners revenue in a day is 3600 coin. Before accepting 3600BTC and making a physical delivery from a source with zero trust I would wait about that long.
The problem is you have assumed a double spender would simply do the obvious thing and try to buy a single very expensive thing. The reality is that a double spender will involve a number of people who are in on the scam and will make many moderate sized purchases. As a bitcoin merchant I have no idea if the 1BTC transaction I have received is part of a set of many transactions which will all be double spent.