do you know the exact expiry date on visitor stamp?

[Mr.Maker]

Hi, do you know the exact expiry date of my visitor stamp?

I got the stamped on the Aug. 24, 2011. and is an expiry date Feb. 23 or 24?
I just submitted online extension application on 23rd with my computer but it is submitted on 24th because it is recorded on EST time....

I'm really worry about my family's extension application. Should I just wait? or Should I send restoration form asap?

Anyone help?

Thanks.