My adults can "hold it" for many hours, will eventually go out back when they are about to burst.
It rarely rains all day long, and even then there are light periods. We run up to the dog park and toss them in, they will pee and poop in about 30 seconds then be ready to get back in the car (we are lucky, the dog park is only a mile from home). I can't drag them out on leash, they just put on the brakes and won't go.
In really bad weather, when it does rain all day, we drive up to a long highway overpass, get out and walk up and down as cars whiz by overhead. The dogs are pretty quick here, too!
Anne in Tampa