Just wanted to add that the level requirement you've suggested for a 4-5 man team is drastically off. We completed this boss fight in 14m and 58s exactly today. I was actually brought here by googling how long the boss fight was, because I was curious to see if we just made it or if we had plenty of time. In total we were a 5 man team consisting of 2 EK's (both level 400), 2 ED's (both level 350) and 1 MS (level 500).
Given what I know now about the 45 minute time limit, I would say you could easily do this with a 5 man team at level 400+, but I dare say even a 4 man team would be fine at that point, as the second EK's damage was negligible during our fight at least.