In the most stupid way: substitute one by one. A=3，B=5，C = 1； A-B-C，3+3+5= 1 1，A-C-B，3+3+ 1=7，

B-A-C，5+5+3= 13，B-C-A，5+5+ 1= 1 1，C-A-B， 1+ 1+3=5，C-B-A， 1+ 1+5=7。

Therefore, the best way is to XiaoDong-Xiao Xia-Xiaoqiu. The total waiting time is at least 5 minutes.