Hello Amlim,

Maybe one possible approach could be if you are using the property HeadTextFormat. In my sample I add additional interval - Week,  with StartRange property - StartDate and following code:

private void ultraTimelineView1_VisibleDateTimeRangeChanged(object sender, VisibleDateTimeRangeChangedEventArgs e)
{
    CultureInfo info = new CultureInfo("en-US");
    Calendar cal = info.Calendar;
 
    CalendarWeekRule myCWR = info.DateTimeFormat.CalendarWeekRule;
    System.DayOfWeek myFirstDOW = info.DateTimeFormat.FirstDayOfWeek;
 
    string weekString = "Week: " + cal.GetWeekOfYear(e.VisibleDateTimeRange.StartDateTime, myCWR, myFirstDOW);
    ultraTimelineView1.AdditionalIntervals[0].HeaderTextFormat = weekString;
}

Please let me know if you have any questions