解决方法一：
TDateTime dt = DateTimePicker1->DateTime;
time_t timer;
unsigned short year, mon, day, hour, min, sec, msec;
dt.DecodeDate(&year, &mon, &day);
dt.DecodeTime(&hour, &min, &sec, &msec);
tm t;
t.tm_year = year - 1900;
t.tm_mon = mon - 1;
t.tm_mday = day;
t.tm_hour = hour;
t.tm_min = min;
t.tm_sec = 0;// 把秒变为0
t.tm_isdst = -1;
timer = mktime(&t);
int year, mon, day, hour, min, sec;
tm *tblock;
tblock = localtime(&timer);
TDateTime dt1(tblock->tm_year + 1900, tblock->tm_mon + 1, tblock->tm_mday);
TDateTime dt2(tblock->tm_hour, tblock->tm_min, tblock->tm_sec, 0);
dt.Val = int(dt1) + dt2 - int(dt2);
DateTimePicker1->DateTime = dt; // 得到结果
