Can I apply for a Non-O Marriage extension 1 month before my visa expires, and when do appointment slots open at CW?

The user asks about the rules regarding the Non O Marriage visa extension at the CW, specifically if they can apply less than 45 days before their current visa expires. They mention their current expiration is on April 15 and they wish to apply in the first week of March due to travel plans. Additionally, they inquire about the opening time for online appointment slots at CW. Responses confirm that it is possible to apply for an extension when less than 45 days remain, noting that a 21-day under consideration stamp will be issued during the process. There is also mention that appointment slots typically open one month in advance.