I can't speak to humidity, but if it's too humid I would think your plaster would already absorb moisture and turn into a brick over time. I wouldn't even consider this a factor.
Curing is a chemical reaction and not an evaporation thing. Plaster gets hot in an exothermic reaction and will dry itself out as it cures and converts the water. Any excess moisture in the air won't matter.
Timing wise on consistency, It's been awhile since I've cast so I don't have it memorized but it's around 10-15 minutes or so. Just sit around and keep poking it every so often and you'll get into the ball park and then can go from there. When in doubt scrape a bit early rather than too late. When it gets too thick sometimes you can run the knife over the top lightly and it will turn the plaster back into a liquid form but that window is very small and the more you play with it, the worse the end result.
Below are my assessments of those molds as I own them all. I would let them all cure for AT LEAST 45 minutes total from pour to demold. Start there and work backwards as some you can pop around 30 minutes. Better to be safe than sorry.
70: Pop early but be careful of long bricks as they can break in half.
71: You WILL have problems with those fieldstone archways. Those always break for me if I demold early. Sometimes those smooth marble column bits break. Not the end of the world if something breaks as you can always glue them. It's more of an annoyance thing.
80: Same problem with columns as 71. they are just really thin and long and brittle until cured but can be removed gently.
85: FUCK this mold. It's awesome for all the cool bits but is the biggest pain the the ass ever. Half those bits don't cast right and the ones that do break when you take them out. Specifically the door halves snap in half. Hollow barrels, broken bucket crate & lid break when taking them out. They are so thin and fragile. The 3 part stone door the tips either don't cast or break when taking them out if you flex the mold too much. Everything else is pretty solid. Pouring into this mold requires extreme care.
One tip I forgot, never pour directly into a mold cavity if you can help it. Pour at the junction of multiple and let it drizzle in slowly and displace all the air. This mold is so small that if you pour right into a space like a crystal, bucket, lid, or any other small space, an air bubble will get trapped and cannot rise out of the plaster. Then you end up with a messed up bit.
203: pop early. Those tiles are solid.
You can't overbake them time wise. The more the better. High temperatures could possibly yellow your bricks though. Low and slow to prevent any potential cracking from moisture expansion.
Temperature wise, I've never done it but I think you can break the chemical bonds if it gets above 400 F. At this point, yes I believe they can turn brittle again and crumble.
Jet dry. I keep a big beer keg ice bucket full of clean water and a small 5 gallon bucket with wetter water. I always rinse completely in the big bucket. Molds, tools, and trays get cleaned there. The wetter water never touched dirty molds. Put your molds in the wetter water and let them sit for a bit.
Doing this all underwater. Get a small brush and work the air bubbles out. Sometimes I use a syringe and forcefully squirt water into the cavities and that gets air out. Once wet and free of bubbles, just shake them off gently and start pouring.
Do not let your molds soak in water overnight. The silicone gets this really weird texture on it and could impact your end bricks. It won't harm the molds. Let it air dry and it goes back to normal.