Considering the light and darkness effects on Zombies:- Throw out the idea of night being a separate setting and focus only on darkness speed enhancement. The difference would be that every difference in light level would affect the zombies, but you can change the highest level of influence, so the fastest they can go from being in complete darkness. So if they do speed up past player speed in total darkness or just Jog or something, the choice is yours.
- Zombie speed would be calculated based off the general lighting in the area (if they're indoors our outside, the weather, etc.), but based off the maximum addition defined when entering world, so for example we have: Very high light -30% of speed addition, regular light (cloudy day, sunlight indoors) no change, low light (dusk, dawn, heavy clouds, cloudy indoors) +30% of speed addition, very low light (moonlit night, unlit indoors) +60% speed addition, no light (dark night, unlit basements) +100% speed addition.
- Take into consideration the amount of light a day generates. Clear sky will have lots of sunlight and will slow down Zs. Cloudy day will generate less sunlight and will get them to regular speed. Heavy clouds with rain will be closer to dusk, almost night, but still visible, making the Zs go faster. Add to that a few timespans of night, when there is total darkness (speed up enemies even more) and where everything is seen in the moonlight (similar to heavy clouds). Indoors would shift the lighting 1 level lower, so if it's sunlight outside, inside it's regular, regular outside will make inside low light, etc.
I know this would require reworking how light works ingame, but it only means it would be harder to implement and perhaps not possible... Still i would find it very interesting to see ingame.