Request - Definitive Sitefinity DateTime

I have switched my code around too many times trying to save UTC times, ToLocal, ToSitefinityUITime ect. Can someone please chip in and let me know how I'm supposed to save a datetime from a RadDateTimePicker to sitefinity's eventStart/eventEnd fields?

Here's my situation. I'm in the US Central Time Zone and have clients all over the US in different time zones. I set their time zone correctly in the Sitefinity settings. I have a front end event submission form.

Default dates for RadDateTimePicker: 

dtEventBegin.SelectedDate = DateTime.UtcNow.RoundQuarterHour();
            dtEventEnd.SelectedDate = DateTime.UtcNow.RoundQuarterHour().AddHours(1);

Persisting the user adjusted dates:

calEvent.EventStart = dtEventBegin.SelectedDate.Value;
            calEvent.EventEnd = dtEventEnd.SelectedDate.Value;


Setting the edit page with the persisted values:
DateTime startDT = calendarEvent.EventStart.ToSitefinityUITime();
            eventDetailCtl.dtEventBegin.SelectedDate = startDT;
 
            DateTime endDT = calendarEvent.EventEnd.HasValue ? calendarEvent.EventEnd.Value : calendarEvent.EventStart;
            eventDetailCtl.dtEventEnd.SelectedDate = endDT.ToSitefinityUITime();

Display persisted dates on detail page:

private string GetEventDate(Event calendarEvent)
        
            DateTime startDT = calendarEvent.EventStart;
            DateTime endDT = calendarEvent.EventEnd.HasValue ? calendarEvent.EventEnd.Value : calendarEvent.EventStart;
 
            StringBuilder date = new StringBuilder();
 
            date.AppendLine("<div>" + startDT.ToSitefinityUITime().ToString("dddd MMM d") + "</div>");
 
            if (calendarEvent.EventEnd.HasValue)
                date.AppendLine("<div>" + startDT.ToSitefinityUITime().ToString("h:mm tt") + " to " + endDT.ToSitefinityUITime().ToString("h:mm tt") + "</div>");
            else
                date.AppendLine("<div>" + startDT.ToSitefinityUITime().ToString("h:mm tt") + "</div>");
 
            return date.ToString();
        

I cannot for the life of me get this correct for every time zone. What am I doing wrong?