Each chicken has it's own timetable, and it doesn't often coincide with ours. I'm not sure why another hen that's already laying would make a difference - the internal workings of the other hens won't change. So much depends on the breeds or varieties of chickens you have. Red Sex Links tend to start early and others like Brahmas take their time - at least that's been my experience. I think egglaying (or not laying) causes a lot more concern than there needs to be. They'll lay when their internal clocks and systems tell them it's time. Oh, and after weeks of you checking nests two or three times a day, changing this and tweaking that, sitting and staring at them, you'll decide to take an afternoon off and head to town, only to find an egg when you get back and no idea who laid it. Silly chickens!!
If you haven't done it already, put some golf balls or fake eggs in a nest. Again, it won't MAKE them lay...but it does show them what those nest boxes are for. Good luck!
