2liveandthai2050

I received a multiple entry visa in Savannakhet just about 3 months ago approximately. My stamp expires this Sunday December 17th . If I go to my local immigration office not until Monday December 18th, will that be considered late, or ineligible for 60 day extension based on marriage? I have a bad case of food poisoning and would prefer to ride it out and just go on Monday. Thanks.