The time something takes to build in PA depends entirely on the buildpower that is used to build it. Two units built with 60 buildpower that cost the same will complete at the same time. So, basically: Unit cost / build power = number of seconds to get it built. A single orbital fabber has a buildrate of 45. It takes 11 m 6 s to build a Helios on its own. An orbital factory has a buildrate of 80. Assuming you don't assist it it will take 3 m 53s to build one omega.