Leaving the control in Champlon you start to go up and down the hills for 185K with 2500 meters to climb. So it all depends on your fitness level I guess.
According the ACP time table, the closing hour of the control in Champlon is 2:08 in the morning. The closing time in the next control (647K) is 9:07. If you leave at 5 you have got 4h to do 90K on hilly terrain. But as I said earlier: I'm not going to check the times with a loupe.
Anyway, the control in Champlon closes at 6 because we have to clear the site before 7 and we have a lot of cleaning to do. Therefore we can not offer breakfast for riders staying elsewhere, sorry.
indeed there is a huge gap between De Panne and Houyet. There are no 24h petrol stations along the route that I know of. 24h stations are rare in Belgium. There are some along the mayor highways, but unreachable by bike. So my advise is to buy what you need whenever you can. There is a petrol station in De Panne, you cross Ieper (171K) and Roubaix (207K). By morning you arrive in Cerfontaine (340K) where a patrol station and a Carrefour can be good places to buy food and drinks.
Keep in mind that the possibility for shopping in the South of Belgium is scarce. That is why I directed the route via towns like Paliseul (SPAR shop), Bertrix, Neufchateau, ...
But hey, BOB is not club Med