Также в .NET есть DateTime.Ticks ..., который может быть немного более точным и работать на XP, если это необходимо ... Пример, показанный на MSDN:
DateTime centuryBegin = new DateTime(2001, 1, 1);
DateTime currentDate = DateTime.Now;
long elapsedTicks = currentDate.Ticks - centuryBegin.Ticks;
TimeSpan elapsedSpan = new TimeSpan(elapsedTicks);
Console.WriteLine("Elapsed from the beginning of the century to {0:f}:",
currentDate);
Console.WriteLine(" {0:N0} nanoseconds", elapsedTicks * 100);
Console.WriteLine(" {0:N0} ticks", elapsedTicks);
Console.WriteLine(" {0:N2} seconds", elapsedSpan.TotalSeconds);
Console.WriteLine(" {0:N2} minutes", elapsedSpan.TotalMinutes);
Console.WriteLine(" {0:N0} days, {1} hours, {2} minutes, {3} seconds",
elapsedSpan.Days, elapsedSpan.Hours,
elapsedSpan.Minutes, elapsedSpan.Seconds);
// If run on December 14, 2007, at 15:23, this example displays the
// following output to the console:
// Elapsed from the beginning of the century to Friday, December 14, 2007 3:23 PM:
// 219,338,580,000,000,000 nanoseconds
// 2,193,385,800,000,000 ticks
// 219,338,580.00 seconds
// 3,655,643.00 minutes
// 2,538 days, 15 hours, 23 minutes, 0 seconds