Important dates in Properties and Transactions are not automatically added to the calendar. In order to get them in your Calendar, you can use a Workflow to assign the Important dates that are important to each user. This prevents less important dates from showing and taking up space on the Calendar of those users on your team which do not need to know them. They will only see those dates which they believe are important to them.
Take a look at these videos for more details on building Workflows!