Yeah I left it open and the check documents window rejected it, so I did a new one and put check out date to the expiry of my rental contract, very bizarre
just apply for the Non O visa before you travel, come to Thailand, open a bank account (easy with a non o) and then when you have 30 days remaining, apply for a year extension, it not hard to do. The people who say it is difficult are the ones that cannot follow instructions and want to argue about the requirements.
If you just do it how they ask it is as easy as photocopying documents and handing them over, Simple