const int numberOfDays = 10;
var startDateTime = new DateTime(DateTime.UtcNow.Year, 5, 5);
var endDateTime = startDateTime.AddDays(numberOfDays);
var start = new DateTime(startDateTime.Year, startDateTime.Month, startDateTime.Day, startDateTime.Hour, startDateTime.Minute, 0, 0, DateTimeKind.Utc);
var end = new DateTime(endDateTime.Year, endDateTime.Month, endDateTime.Day, endDateTime.Hour, endDateTime.Minute, 0, 0, DateTimeKind.Utc);
Console.WriteLine($"start: {DateTime.MaxValue.Ticks - start.Ticks:D19}");
Console.WriteLine($" end: {DateTime.MaxValue.Ticks - end.Ticks:D19}");