These docs are for an old release. Info on upgrading to v6
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nowIndicator

Whether or not to display a marker indicating the current time.

Boolean. default: false

The indicator will automatically reposition itself while the user is viewing the calendar.

When set to true in one of the TimeGrid views (view live demo):

timegrid view now-indicator

When set to true in one of the timeline views (view live demo):

timeline view now-indicator