Another thing to watch out for, anywhere that is shaded part of the day, like along hedgerows, will stay wet much longer than the rest of the field. If at all practical, that is better saved for the next day. Though we did small squares for horse people, so sometimes we just baled and tossed the bale or two from that part on the compost pile, or fed right away, depending on the details of the situation.
When baling, watch out for dew, or even just the cooling down at the end of the day bringing moisture back out of the air. There'd usually come a time on baling day between 6:30 and 7:30 that the moisture would go back into the hay. It got tougher, bales got heavier, and usually everything baled after that point molded. Unless it's going to rain, bale it tomorrow.
Speaking of rain, it's not necessarily an issue, depending on how much, and how recently it was cut. The same amount of rain that would ruin hay on bale day would be just fine if it wasn't too long after cutting and the hay didn't dry out yet.
Tedding also works wonders when you have good drying weather. We've cut and baled same day on rare occasion. Definitely helps keep the hay from bleaching, but the weather has to be hot enough, dry enough, and breezy enough, and you have to run the tedder through it 3 or more times, but if you have the help available or small enough fields, it makes some really nice hay.
As for knowing if it's ready, I like to grab a pinch and taste it. Kind of hard to explain, but if you've chewed on a bunch you'll know what too dry, too wet, or too dusty will feel and taste like. I've found if it tastes good to me, my handful of cattle will eat it up and yell for more. If I can't stand chewing on it for a few minutes, neither can they and it winds up all over the place and most is wasted.