I flew from RHO a couple of weeks ago, not that early, though. As described by East_and_West, there should be no problems, lines at A3, especially the *G counter are usually very short compared to the seasonal flights of tourist-catering airlines. There is a longish walk after CI, but not really problematic. At any rate, usually taking the 6:40 A3 flight from HER (worse airport than RHO) I can tell you that you should have no problems arriving at -70', even at the peak of the high season. By the way, the reason for the very long lines is the fact that tourists are bussed to the airport at around -120' to 150'. Imagine ~200 passengers of an A320 all arriving together for CI, often using only two counters.