1 procedure TForm1.Button8Click(Sender: TObject);
 2 var
 3   sd, nd: TDateTime;
 4   randid: string;
 5 begin
 6   sd := StrtoDatetime ('1981/08/08 00:00:00');
 7   nd := Now;
 8   Memo1.Clear;
 9   Memo1.Lines.Add('开始测试时间差:');
10   Memo1.Lines.Add('起始时间:1981-08-08 00:00:00');
11   Memo1.Lines.Add('终止时间:'+DateTimeToStr(nd));
12   Memo1.Lines.Add('年:'+IntToStr(YearsBetween(sd, nd)));
13   Memo1.Lines.Add('月:'+IntToStr(MonthsBetween(sd, nd)));
14   Memo1.Lines.Add('周:'+IntToStr(WeeksBetween(sd, nd)));
15   Memo1.Lines.Add('日:'+IntToStr(DaysBetween(sd, nd)));
16   Memo1.Lines.Add('时:'+IntToStr(HoursBetween(sd, nd)));
17   Memo1.Lines.Add('分:'+IntToStr(MinutesBetween(sd, nd)));
18   Memo1.Lines.Add('秒:'+IntToStr(SecondsBetween(sd, nd)));
19   Memo1.Lines.Add(#13) ;
20   Memo1.Lines.Add('以秒差为例生成随机数: ');
21   randid := IntToStr(SecondsBetween(sd, nd))+
22             IntToStr(random(9))+
23             IntToStr(random(9))+
24             IntToStr(random(9))+
25             IntToStr (random(9));//呵呵，很笨的方法。
26   Memo1.Lines.Add(randid);
27 end;

结果如下：
开始测试时间差:
起始时间:1981-08-08 00:00:00
终止时间:2020/3/7 15:17:37
年:38
月:462
周:2013
日:14091
时:338199
分:20291957
秒:1217517457
以秒差为例生成随机数: 
12175174571070

 1 function GetSubDateTime(S1, S2:string): string;
 2 var
 3   T1, T2: TDateTime;
 4   D, H, M, S: Integer;
 5   Value: Int64;
 6 begin
 7   T1 := StrToDateTime(S1);
 8   T2 := StrToDateTime(S2);
 9   Value := SecondsBetween(T1, T2);
10   D := Value div SecsPerDay;
11   H := Value mod SecsPerDay div SecsPerHour;
12   M := Value mod SecsPerDay mod SecsPerHour div SecsPerMin;
13   S := Value mod SecsPerDay mod SecsPerHour mod SecsPerMin;
14   result := Format('%.2d天 %.2d:%.2d:%.2d',[D, H, M, S]);
15 end;

输入2020/03/06 14:39:32
输入2020/03/07 15:40:34
结果如下：
01天 01:01:02