Hi,
There is not a way to do that in in the free event calendar that ships with mojoPortal.
However in Event Calendar Pro it is possible by setting the begin and end time to the same value then adding this in user.config:
<add key="EventCalendarPro:ListViewHideTimeIfBeginIsTheSameAsEnd" value="true" />
<add key="EventCalendarPro:DetailViewHideTimeIfBeginIsTheSameAsEnd" value="true" />
Hope that helps,
Joe