Germination can occur as early as 2 -3 days, but it may take up to a week or more for he first signs of germination to show.
Please note that some have had to wait up to 3 weeks to see growth in some jars.
It depends on a multitude of factors - some of which are: temperature, substrate, spore concentration, age of the spores, etc. There are so many different relevant factors it is very hard to determine within the 1st2 weeks why you have not shown germination. Give it at least a week before you worry, and at least 2 weeks before you panic. All you need are 2 spores to germinate and take over the entire jar - and luck is on your side when proper procedures are followed.
Please be patient and do not panic after only 2 days, no matter how fast you've read other people's colonization was. Their setup, factors, everything varies just slightly from yours. Now, after a period of time with no germination, analyze all of the possibilities (such as temperature, water content, sterilization procedures, etc.) that would hinder growth. This is your best bet on learning the life cycle, and also learning the peculiarities of your personal setup (as far as variations go).