Caulk is an essential component of any quality exterior paint job.
Besides sealing up and thus keeping water out of open joints, caulk helps gives a paint job a clean and crisp appearance.
Alas, most paintable silicon/acrylic caulks need to dry for several hours (or better yet, a full day) before you can paint over them.
Alex Fast Dry from DAP cuts drying time to 40 minutes or less -- allowing you to caulk something and then paint it just a short time later.
I've used this relatively new product several times recently.
It's thicker than regular caulk, and it starts to skin over in just a few minutes. This makes it slightly more challenging to apply smoothly than most caulks.
But the time savings are worth it.