Well, you've already got two takers, but in case those two don't work out, I'd be more than willing to help. I write my own stories sometimes, and while I've never posted a story for Hetalia, it is THE fandom in my life right now. Strictly speaking, I have beta'd before, but... the person I was doing it for had no grasp of plot, dialogue, continuity, or heck, even grammar... But I've been itching to do a USUK story, so editing/ co-authoring one would be great since I seem to be too lazy uninspired to complete one on my own. Time zone differences shouldn't matter too much- I'm American, but I tend to keep odd hours, and I am often on very late at night (which, I suppose, would be sometime in the afternoon for you?) I am very picky with grammar/formatting, so I could definitely help out if you have trouble with English. (Which doesn't seem to be the case, but, it might not be your first language, and that can be hard... *is studying German herself* )
So, just let me know if you decide to use me or someone else!

P.S. Just out of curiosity, what kind of story will this be? AU? Gakuen? Cardverse? Or something else?