The total hashrate is affected the first 2-5 minutes of mining because the gpu's doesn't start to work.  If you open gpu-z you can see that only some of the gpu's are working. This isn't a problem if you mine at the same pool for a long period of time. (If all the 6 gpu's have started).
But it is a problem when you use it with a profit switcher software like the Nemosminer, minercontrol, nicehash(3rd party) or similar software.