Marine caulks cure by absorbing moisture from the air. According to 3M, spraying water on most of their marine caulking products will accelerate the curing process. This is especially true with silicone-based caulks.
Many of us purchase a small $8 tube of caulk to fill a few screw holes, and then find that the tube hardens in just a few days, rendering it useless for another job.
To avoid this waste, I put the tube in a Ziploc bag filled with a large quantity of desiccant material, using both packets and tablets. You can find these little items packed in medicine bottles and electronic devices. They are often labeled, ―Do not eat. Drug stores throw them away by the handful. My pharmacy saves them for me. This material is also available for purchase, for a nominal price, on numerous commercial packing websites.
Desiccant material absorbs the moisture and slows the caulk‘s curing process. By putting a tube of caulk in a Ziploc bag, along with desiccants, and then in a sealed glass jar, my caulk stays fluid and useful for two or more years.