Do I have to wait 60 days before applying for a 12-month extension on a Non-Immigrant O visa based on my bank deposit?

If your bank account is already set up, send the money now. Also, apply for a Non-O while abroad.

400k is for the extension of stay for marriage only

No, you don't wait 60 days. You wait TWO MONTHS. Whether that's 60 days or not depends on the length of the months.

If you make your deposit on the 12th of a month, you can apply on the 12th subsequently 2 months later. So February 12th means you can apply April 12th, etc.

Also, you cannot apply earlier than when you have 30 days left on your entry stamp from your non-O, though some offices allow when you have 45 days or less left.

two months not 60 days