'Congested' servers are slightly different than when servers are temporarily closed for character creation.

If a server is congested, it'll remain congested and completely closed off to character creation until Square manually changes it back to standard world state in a later maintenance which is when they usually like to do it. The 'seeing servers uncongest randomly through the week' isn't the same as a congested server; when servers have enough players still logged in, their character creation will be temporarily locked until the amount of online people gets under a certain number; but they are still standard servers.

As Behemoth is congested, your best bet is to make a character on a different server within the Primal Datacenter, and just wait till behemoth is returned to a standard server state, then transfer your character over there. Till then, you can world visit behemoth, and if you want to chat with people from there, you can make a cross-world linkshell.