Experts might have the answer for this question.
Some info here:
Rights and Duties of a Taxpayer | The Revenue Department (English Site) (rd.go.th)
Personal Income Tax | The Revenue Department (English Site) (rd.go.th)
Thailand Tax Return Filing Deadlines - SHERRINGS
5. Tax Payment
Taxpayer is liable to file Personal Income Tax return and make a payment to the Revenue Department within the last day of March following the taxable year. Taxpayer, who derives income specified in c, d or f in 2.3 during the first six months of the taxable year is also required to file half - yearly return and make a payment to the Revenue Department within the last day of September of that taxable year. Any withholding tax or half-yearly tax which has been paid to the Revenue Department can be used as a credit against the tax liability at the end of the year.
4. Application for exemption or reduction of fine and surcharge
A taxpayer has the duty to file his tax return and pay proper taxes on time. Should he fail to do so, he will be subject to fine and surcharge on top of the tax due. However, on some special grounds he may request for exemption or reduction of fine. A tax officer does not have the power under any law to exempt or reduce surcharge. Only in the case where the Director-General grants an extension of the time period of tax payment or remittance and such tax has been paid or remitted within the extended time period, then the surcharge may be reduced to 50% thereof.