When does the extension start when applying for a visa extension in Thailand?

Hi everyone, asking for a friend on the basis of visa exempt. Free 60 days and they want to extend for the 30. If they go to immigration let’s say a week before the full 60 is up, does the extension start from the time they go to the office or the time that the 60 days will expire? I remember it being when you go to the office, but reading mixed results online. Thank you!