Due to the timing of missile being fired during the fire phase and detection (1st thing in the fire phase) a missile is invisible for the first 5 seconds of flight. This translates to your beam point defense will NEVER fire on a missile during those 1st 5 seconds.
Realistically most beam warships use beam PD weapons, which are only really usable in “final fire” mode. The flight time of enemy missiles is not really important for final fire, and final fire will always get a shot, even if the flight time of the enemy is lower than 5s, no?
I was under the impression that Final Defensive Fire was always allowed to fire upon incoming warheads, provided that the ship in question still had unallocated energy weapon fire from weapons mounts dedicated to Final Defensive Fire.
Also, if an energy weapon based fleet is attempting to close a large distance through the range envelope of an opposing force, wouldn't the fleet be better off with at least some of its weapons dedicated to Area Defense, in stead of Final Defense? As I understand things, Area defensive fire allows ships to engage previously detected missiles during the standard shooting phase, and will engage any detected missiles in range. Final Defensive Fire, on the other hand, works on the same basic rules as the Close In Weapons System.
If an energy focused fleet does not have enough individual weapons mounts to safely divert some of them to Area Defense, then the fleet has already lost, as none of the ships may support other fleet elements, which makes the particular energy fleet a waste of research and resources. If the fleet does have enough energy mounts, then the fleet is approaching the appropriate size for dealing with the given threat.
And, like all fleets, the larger your Resolution 1 sensor is, the happier you are. With sufficient detection range, energy weapons may attempt to swat down missiles in Area Defense mode, instead of depending upon Final Defensive Fire. With sufficient detection range, and sufficient research, your fleet can also have nice bonuses towards tracking and targeting missiles.