Re Nocturnal: May well add an opposing perk, undecided yet, and how exactly it would work with having both of them.
Well as I see it from the description it would cost two perk points and the unit experiences both cons & pros at both times day & night. Though nobody says it has to do the same thing. I would actually like, in case you decide to have both, if they can go into different directions. As if fitting different play styles. And if having both perks could differentiate day vs. night gameplay even further for such party member, favoring who is able to adapt.
I dunno, an example close to what you implemented (just changed cons of Nocturnal):
Nocturnal (+1 AP, +10% damage, -10% damage taken at night | -10% damage during day) -> +/- 20% dam night vs. day
Diurnal (+2 initiative, +5% CTH, +5 evasion during day | -5% CTH at night ) -> +/-10% cth day vs. night
Though I'm not married to this exact setup, not sure how it will play out.
Re Critical Charge: It will stack until you make a critical hit, and once you get a critical, it goes back to the baseline crit chance of your current weapon. It's independent of weapons, so you can switch as needed.
Statistically overall it's not so far away from flat % crit chance boost, such as like More Criticals perk in FT (flat +5%). Closer difference is that we either have higher chance later (charge) or more from early on (flat chance increase). Depending I can imagine shooting with pistols and later switch to precision rifle.
Additionally, you can charge crit chance as well as crit damage with this perk -> would make somebody with low initial crit chance bigger hitter when it lands eventually, as he accumulates higher crit. damage. (is it 150% of base dam? then what about +5% each hit till it crits, or so?...)
Was thinking to ask, whether you're considering to do something with Precise Strike perk (+3% crit chance with bladed weapons)?
I would propose to boost it significantly or better use there more general effect of the More Criticals perk (+%5 crit chance, req. just lvl?) mentioned above instead. This can be take up to 3 x in FT IIRC. So it's also good candidate if you would be open to let us take some perks more times. If somebody takes also charge, that would be serious commitment to criticals as it will all cost 4 perk points.