Actually, you can adjust the cloaking time, but it’s a bit indirect. Here are the important variables (duplicated from the GSB Modding 101 Guide at the top of this forum):
cloak_consumptionrate - How quickly the cloak drains the power
cloak_rechargerate - how quickly the cloak regains power
max_cloak_power - maximum power capacity of the cloak
On the vanilla Camouflage Shield, the first two variables are the same. This means it takes the cloak just as long to charge up as it does to run out of power - the ship will be cloaked half the time (providing it doesn’t decloak to shoot at people). You can use these to adjust the proportion of the time that the cloak will be on - high recharge/low consumption will be cloaked longer than visible, low recharge/high consumption the opposite.
The third variable affects how much power the cloak has - the larger this number, the longer the period of recharge/cloak. I believe that a cloak will enter the battlefield completely discharged, so if you make this number high but don’t increase the recharge rate appropriately, it will be a long time before your cloaking device kicks in.