5 years to me sounds like the time it would take to have all three vessels built and in operation. Everything I've seen says about 3 years +/- a few months. At some point, there will be construction going on on all three at the same time, just in different phases. The 3rd has potential to be built in a US shipyard according to the MASGA "agreement" (not even sure if that is still a valid agreement, just remember it being heavily hyped by SK).
(Mr. C quotes Delfin at 4 years, I'm hope it's quicker than that)