I also tried this, but without success.

[PXDBDateAndTime(UseTimeZone = true, PreserveTime = true, DisplayNameDate = "Scheduled Start Date", DisplayNameTime = "Scheduled Start Time")]
[PXDateTimeSelector(Interval = 15)]
[PXDefault]
[PXUIField(DisplayName = "Scheduled Start Date", Visibility = PXUIVisibility.SelectorVisible)]
public virtual DateTime? ScheduledDateTimeBegin
{
    get
    {
        return this._ScheduledDateTimeBegin;
    }

    set
    {
        this.ScheduledDateTimeBeginUTC = value;
        this._ScheduledDateTimeBegin = value;
    }
}