Well, if you don't have permanent golden time, you're missing on a lot, that's all i can say :/
Also, you can only achieve permanent golden time again at Lv49 with 40% CDr~ish
Apparently the cooldown doesn't go past 40%, but it counts 40% from the original Lv1's cooldown and deduct it from your current skill level, and since FM2's CD reduce per level, it makes us think its not capped at 40%, that or it has 50% cap or something :/ all i know is that the % is only related to the Lv1 skill's CD.
But yeah, naturally, you can argue with physical, magical J build or even hybrid, but golden time again will always give you Lv3~4(on awakening) SAC from basic attacks and some skills IN addition to +85% critical damage to both magical and physical, so regardless of your build, golden time again is always good.
I don't see why it wouldn't be a general rule to GDA loop :C
Either way, no matter what character you play/gear you use, you should be able to get 40%~ CDr from PNAs and tunings & costume set effect / additional module/shield set effects.
You just prioritize a CDr option cube for FM2 on J since it makes you able to loop FM2 at a lower level..
My favorite build for a Lv~50ish J:
FM CDr cube for FM2 and a lantern, 3x hybrid modules that gives critical rate, preferably at Lv60 elite airport module (+6% critical chance), of course for hybrid build (and you'll have almost 0 physical defense xD full retard build that is)
In total: 42% critical chance 33% CDr and 10~14% FM2 CDr on option cube.
Higher critical rate means better profit from golden time again AND lanterns, its hard without plane gate gears so..