I would like to un-check the following option to show events from Evolution calendar in the time & date indicator but it is grayed out. Evolution is not installed on my system.
The indicator regarding your question is called
indicator-datetime, the following command should disable showing upcoming events:
gsettings set com.canonical.indicator.datetime show-events false
This setting could also be found via
dconf-editor, which i can only recommend as it has a search option.