This is a bit from one of the posts, pretty much answers
"If you want the things to go quickly, come on Monday or Tuesday at Aubagne, you will be bleu in the same week, and next Thursday will go rouge or go home. I came on a Monday, Tuesday I had medical, sports and IQ tests, Wednesday I was selected for blue, and the next week I did not pass the commission for rouge. I spent exactly 10 days in Aubagne;"
Before an admin locks up the thread, It has to be pointed out that that is one man's story. there are no set rules that must be followed to the letter. It would be a bit daft to say that exactly ten days that you will know if you are accepted or not. So you can then book your return ticket on the 11th day after arriving in France.
Besides it isn't as though you are coming from that far away. You can either get yourself an open ticket or just take enough money for a return ticket.