How Does the O Non Immigrant Single Entry Visa Work in Terms of Validity and Entry?

as people correctly stated you have 3 months from the date the visa is issued to ENTER thailand, when you will be stamped in for 90 days like everyone on a Non-Immigrant single entry visa.

There is an "enter before" date on your visa sticker. You must enter Thailand on or before this date. You will get 90 days upon entry and the clock starts ticking the day of entry.

You can use the visa for three months from the visa issue date and you will get a 90-day entry stamp starting on the day of entry (which will be counted as day 1 of 90).

So unless there is a chance that you will have to delay your arrival until sometime in March there is no reason to delay getting the visa. Just plan it in for when it is most convenient for you.

Also remember that if you are using the online system and intend to submit your passport personally, rather than by post, there may not be any appointments left when you want them if you wait to book one.

However, when using the online system you can book your appointment well in advance if you want.