=B4-B3,并把目标单元格的格式变成：
以小时为单位:=TEXT(B4-B3,"[h]")以分钟为单位:=TEXT(B4-B3,"[m]")以秒为单位:=TEXT(B4-B3,"[s]")
直接一减啊。。。不过格式得设置成时间长格式
