Which immigration office should I visit in Nonthaburi to request a 30-day exemption extension, and when can I apply for it?

The user is in Nonthaburi and is inquiring about which immigration office to visit for a 30-day exemption extension and the timing for the extension request. The community members confirm that the Nonthaburi immigration office is the correct location and indicate that extensions can be requested when there are 30 days or less remaining on the current exemption.