var 
datetime1, datetime2:     Tdatetime;
year,month,day,h,m,s,ms:  word ;
begin... ...decodedate(datetime2-datetime1,year,month,day);  
//将两日期相隔数的年月日分离出来
decodetime(datetime2-datetime1,h,m,s,ms);
//将两日期相隔数的时分秒、毫秒分离出来
caption:=datetimetostr(datetime2-datetime1);
//将两日期相隔数显示出来