If I enter Thailand on February 8 with a Visa exemption, will I have until April 8 to leave after extending for 30 days?

If I go to stamp into Thailand on Feb. 8, with the 'Visa exemption' stamp and extend that for 1,900 Baht for additional 30 days, does that make my permitted date April 8? I am planning a trip and my flight out of Thailand will be on April 8, so I am wondering if I stamp into Thailand on February 8, if I will have my days lined up correctly.

And another thing I want to confirm... I read that if your Visa date says 8, and you stamp out on the morning of 9, do they still charge you 500 baht for overstay or is it true they have a 24 hour period where if it's less than 24 hours they will stamp you out as normal without penalizing you? Or is this completely up to the officer?