im going to apply for an settlement application for my GF/soon to be wife in the next week or so.

we are getting married in thailand and then applying for the visa, do i need to get her ID card and passport names changed before applying or can i apply with her maiden name?

if i have to change them, how long does it take and... how?

You can use the old passport but you could possibly encounter difficulties down the line, bear in mind that not all wives want to change their names these days.

Passports only take a few days and ID Cards can be issued on the spot, providing they have them in stock, there have been instances where offices didn't have the blank card, but I don't know if this is still the case.

There is no obligation under UK law (or Thai law, I think) for a wife to take her husband's name upon marriage.

So applying in her maiden name will not be a problem; your marriage certificate will show that she is your spouse and the visa will include the words "spouse of (your name)."

However, if her intention is to take your name and change her passport and id card then it will be simpler to do so before applying for her visa; particularly, as the old git says, changing them wont take more than a few days.

my wife applied for settlement visa in maiden name and has always kept everything thai in maiden name, her uk citizenship and uk passport are all in her married name, has not caused us any problems along the way.