"Datetime.Now giving me datetime in 'MM/dd/yyyy hh:mm a' format"
No, it doesn't.
It gives you an DateTime value - which is a number of ticks since a specified moment in time. Your system is converting the DateTime value to a formatted string using the current system locale when you call ToString on it.
So instead, just use the value:
DateTime saveNow = objCalendarFields.EventDateTime;
Or
DateTime saveNow = (DateTime)objCalendarFields.EventDateTime;
depending on the declaration of EventDateTime.