I don't think it would take 6 months, Moving parts wise 3.24 had a lot more stuff. 4.0 is basically a copy paste Stanton system with a different theme so nothing difficult there so it's "just" server meshing that is now the next hurdle and going by the tests they've done so far it's very impressive stuff.
With the amount of time that's passed since the last test I'm hoping, Considering it's a completely different team to 3.24, That progress is quite far along and the finish line is in sight.
I'd say Evo testing of 2 months should be enough to iron out any issues. 3.24 which had a lot more moving parts what with the inventory reshuffle, Cargo, Hangars etc... took 1-2 months so probably the same again for 4.0, Maybe even less if it goes well.