Your USA sim card phone plan starts on the date you specified in your order, and expires at 11:59pm on the 30th day.
Please see the further information below for more details:
Screenshot below is from the www.usaprepaidsimcard.com.au website order page
Screenshot below is from the the set-up instructions that were emailed in your order confirmation email, and reference on the white sticker on your actual sim card (with the white sticker on your actual sim card stating "You MUST immediately go to: http://tinyurl.com/sim88 to read about your sim card or it won't work properly in the USA!"
