Start a new job knowing you going to another job when you get call up

I accepted a position with a company. They want me to start on the 19th. Week before the start on the 19th another job offer me a position that has better pay(36k) and benefits. But they catch is job two could call me in week or in six months just depends on how long it take to clear my background, how long till next training school class start and if they still need me at the local hub. They told me not to put in my two weeks till I get the green light(once everything clears and I get both spot at training classes and job spot). So what would you do? Start job one and just wait till job two ready and quit in week or six month whenever it is or tell job one about the situation see if they still want me to start with them.