=TEXT(TIME(HOUR(A1),MINUTE(A1)+RANDBETWEEN(15,30),RANDBETWEEN(0,59)),"h:mm:ss")...
=TEXT(TIME(HOUR(A1),MINUTE(A1)+RANDBETWEEN(15,30),RANDBETWEEN(0,59)),"h:mm:ss")A1单元格输入一个时间,在A2单元格写入这个公式,下拉即可!!!