Here are the battleships buildtimes equivalent in minutes, by an unassisted t3 naval yard:
- 5 minutes = 18000
- 6 minutes = 21600
- 7 minutes = 25200
- 8 minutes = 28800
- 9 minutes = 32400
- 10 minutes = 36000
(for reference, a destroyer, at 10000 buildtime, by a t2 factory = 4 minutes 10, and 2 minutes 46 by a t3 factory).
I guess it's possible to leave destroyers as they are and increase further the battleships buildtimes to 7 or 8 minutes, but I think after these values, engy spam assisting (30-40 engies) would be mandatory to build battleships at a good pace, and mass destroyers production would probably become the best strat.
No matter which values are chosen, I think it's a good idea to keep the Cybran battleship with a lower builtime of 1 minute compared to the battleships of other factions.
Last thing : don't forget that Aeon has a tremendous battleship now with the Tempest, that's another reason why I think it's not a good idea to increase buildtimes of battleships too much compared to experimental values. If the Tempest has 12000 buildtime and a normal battleship 36000, Aeon will rule the seas, plain and simple.