Is it even possible to send many waves at the same time/second?

I know we can use camp time, but that means only one wave can appear in enemy report in a second. As it takes time to move to another city and and send second wave. I saw a you tube video capture of some one sending waves from 3 cities just spamming to appear in enemy report almost same second. I am not sure how this is humanly possible.. can some one throw some light in to this?