I am on a non o multi entry visa and my present 90 day stay expires on 24th. I will have to leave Thailand on or brfore the 5th of march so do not want the hassle of a border run, can anyone tell me how many days extension I would get if I applied to the immigration office in Pattaya?

Nothing. You need to do a border run.

Unless you are married to a Thai national or have a child with Thai nationality, than you can get a 60 day extension.

do not want the hassle of a border run

I have never done it, but a friend always books well in advance with Air Asia to KL return, he says you pay less then 3,000 baht, and your back in BKK within 4 hours, swears he will never do a Bus Boarder run again.

Just to clarify my multi entry visa is valid until September it is just that on this visit my 90 days will be up on 24th. From what you have said Immigration no longer extend 90 day visas unless as stated I am married or have kids?

With a ticket out within 7 days they would likely provide an application for extension of stay that is dined after 7 days (normal 1,900 baht cost). 90 day entries do not have to 30 day extension of stay that tourist visas allow.