Entry stamp on Single or Multiple Entry Tourist Visa is always 60 days with possibility of one 30-day extension per each entry of 60 days. No difference on the maximum length of per stay.
, Don't forget to tell to the officer about your travel plan during under-consideration period when you apply for an extension. There is a chance the officer(s) may contact applicant during u/c. If you skip the contact, you might get a risk to lose the application.
As long as you apply for a one-year extension based on the same reason as the current one, your next extension will be added to the current extension, which means it will be 10 August 2025 - 9 August 2026, regardless of how early you apply. You don't lose any day to apply early, no worries.
Sadly, One Bangkok is not your option if you need to do a 90-day report in person unless your visa/extension is issued there. In Bangkok, the area of responsibility of each office is clearly defined. You must go (or send documents) to the office that issued your visa/extension for your 90-day report in person. (except Non-LA)
, You definitely want to ask them, bringing your travel information.
Jomtien has a 30-day application window in advance. If I remember correctly, Jomtien can give you extra days in the application window in case you show proof that you will not be in Thailand the whole of the standard 30-day application period. It could be up to 40 days in advance or so.