var
  Stopwatch: TStopwatch;
  Elapsed: TTimeSpan;
....
Stopwatch := TStopwatch.StartNew;
DoSomething;
Elapsed := Stopwatch.Elapsed;

要以秒为单位读取时间值(例如,从时间跨度),请执行以下操作：

var
  Seconds: Double;
....
Seconds := Elapsed.TotalSeconds;