Can I extend my visa at immigration on the day of expiration?

You should go well before your due date. At least a week or more, to be on the safe side. Leaving it until the last minute is asking for trouble, if there any issues with your documents.

And going on the same day as your last day is asking for trouble. If you're missing a document, you're screwed.

The extensions will be added (top-up) to your current stamp unless you change the reason from your current stamp. If you are applying for an extension for same reason for current stay, you can apply for it in advance, still you don’t ”lose” any day. No need to wait until the last day of your current stamp.

For what purpose do you have a visa?

Did you enter Thailand with a tourist visa issued by a Thai Embassy or Consulate outside of Thailand ? AND was stamped in for 60 days?

Or did you enter Thailand Visa exempt on arrival

And was stamped in for 30 days ?

Retirement Visa?

Tourist Visa ?

Marriage Visa?

Or an extension of stay ???

AND why wait until the Day before your permission to stay expires?

Have you asked your local Thai immigration office for their list of requirements for the Visa you are wanting to extend?