As zigs said, if they've got adequate drainage then being out in the rain shouldn't be a problem. That said I once lost a potted schefflera to excessive rain. However it had recently been defoliated, so its water requirements were less than normal and it was out in continuous rain for three or four days. The rest of my plants, which were full of leaves, handled that rain just fine.
Whether to leave watering before the rain really depends on your weather as well as how exposed your plants are. If our weather is cool when it rains then I may leave off watering for a day or two. However in my city it can be pretty hot immediately before or after a shower, and to complicate matters many of my plants stand close to walls, some with a slight roof above them, so in hot weather I will water them regardless of the rain.