I'm hitting day 7 right now and night hours feel alot more dangerous in A18 than A17. I feel like spawns are higher, I've heard/seen multiple wandering hordes at night, and I'm much more likely to be heard in my base at night than in A17 if I'm not careful. On Day 5 I went out just after 4am and to my surprise a wild feral zombie sprinted up to me and smacked me in the face. I know it was feral from the exp, morning chime sound, and the fact all other zombies were walking. I had not hit her yet so it wasn't rage mod either :P.
I've died twice due to the increased night presence so far (not helped by the fact im in the snow biome so it's alot of lumberjacks). Just dropping a warning here to other folks lol. If you're going to do things at night in A18, FFS be careful, these zambies are not playing around :P.
I don't think it's a problem, but it's definitely being an adjustment for me right now. I could piddle around in A17 at night with near impunity.