I would lay them on their sides with plenty of room for air to flow around them for 3 weeks. Check temperature and moisture, daily.
I agree--3-4 weeks with about 6" between them. If you could, store them inside for that time (depends on your facilities.
I would also lay them on their sides, not the ends. If they get rained on, the netwrap will shed most of the water when they are on their sides whereas the flat end absorbs the rain.
If in doubt when feeding to horses, take the net wrap off and then peel off the outer wrap or two until you get down to good hay. (I've done this many times.) You will be wasting some hay especially the bottom parts which will tend to be wetter. I have spread the top parts out and the horses pick through it, eat the good stuff and skip the moldy. (Assuming they have plenty of food, they won't eat the moldy stuff.)