When God created the world, was each day a period of 24 hours?
No, Creation occured before the sun and the moon were in existance, and each day of creation was a long period of time, for example, we are still living in the seventh day of creation in 24 hour time.
This Q&A was found on Archangel Michael & St Bishoy Coptic Orthodox Church : http://www.stbishoy.org.au/modules/smartfaq/faq.php?faqid=29