How soon can we apply for an Extension of Stay for a 60-day tourist visa in Thailand?

You can apply for the 30-day extension of stay at most immigration offices when you have 30 days or less remaining on your visa. Since your son's 60-day tourist visa expires on June 28th and he plans to fly out on July 1st, you should apply for the extension now. For those in Bangkok, the main immigration office is located at the government complex on Chaengwattana Road. Additionally, local copy shops can assist with necessary copies and filling out forms.