AbyssalCraft-1.11.2-1.9.4-pre-2.jar
compatlayer-1.11.2-0.2.8.jar
incontrol-3.5.5.jar
mcjtylib-1.1x-2.3.11.jar

Here a potentialspawn:
{
"dimension": 0,
"mindifficulty": 1.0,
"maxlight": 4,
"mintime": 18000,
"seesky": true,
"maxcount": "30,abyssalcraft:shadowcreature",
"mobs": [
{
"mob": "abyssalcraft:shadowcreature",
"weight": 5,
"groupcountmin": 1,
"groupcountmax": 2
}
]
}

for the spawn.json:
{
"mob": ["abyssalcraft:shadowcreature"],
"dimension": 0,
"result": "allow"
},
{
"result": "deny"
}

Here is the problem:
For me it seems that there is a %24000 missing somewhere.

An example
/time set 15000 --> mobs should not spawn and they do not -> fine
/time add 24000 --> mobs should not spawn and they do -> broken

now we add a maxtime to the potentialspawn "maxtime": 18000, and remove the mintime
/time set 15000 --> mobs should spawn and they do -> fine
/time add 24000 --> mobs should spawn and they do not -> broken

ok, after waiting 24000 ticks I can confirm that it still does not work^^

That seems that MC is not following its own guidelines then. I can work around it in InControl

That would be wunderful.
Ok, lets go on in this issue thread:
mobs don't seem to spawn with maxlight: 3 and seesky: true
without seesky they only spawn under trees.

Is the minimal block light 4 in the night? I was hoping that the hardcore darkness mod does set the block light to a real 0.

You should be able to see the actual light level with F3

BL is 0 and skylight 15.

Tested with:
{
"dimension": 0,
"mindifficulty": 1.3,
"maxlight": 2,
"seesky": true,
"angry":true,
"maxcount": "30,minecraft:skeleton_horse",
"mobs": [
{
"mob": "minecraft:skeleton_horse",
"weight": 5,
"groupcountmin": 1,
"groupcountmax": 1
}
]
}

and

{
"mob": ["minecraft:skeleton_horse"],
"dimension": 0,
"result": "allow"
},
{
"result": "deny"
}

with maxlight 4 --> spawns with maxlight 2 ---> not a single spawn

Hmm can you look at the ground and take a screenshot then? Also use one of the light overlay mods which show the number (like 'F4' for LightLevelOverlay)

Weird. No explanation for that.

Just you know. I removed Hardcore Darkness to see if its a mod interaction problem. But it doesnt seem to be one. Block light stays at 0.

I don't see how it maxlight 2 vs 4 can make a difference is the light is 0. That doesn't make sense

Its also interesting that blocklight stays at 0 when its noon^^

In the end its not a huge problem. My goal was to reduce the needed blocklight to prevent the standard torch spam.

With maxlight 1 and without seesky they spawn, but only under trees or structures. Seems there is some kind of hardcoded night sky light or something.

Seems to be a bug in the time add command itself as that worldTime value is not allowed to go beyond 24000.

ok, I started testing with:
"mintime": 16500,
"maxtime": 19500,
and did /time set 17000 the mobs did spawn
now I simply will let the game run by itself, results in ~20min

I know its been like a year, but this is still happening for me too. mintime and maxtime only apply to first 24000 ticks

Edit: also happening with Fxcontrol

I will fix this

Fixed in latest version