@Chandreshn ji
Crystals absorbs negative energies and they need cleaning and again charging from time to time.
Same is for gemstones, while VK is such a tool which is once attuned by @"Sharat Sir-VK Inventor" ji it remains charged for its lifetime till you melt it in a furnance.
As per your query every request to VK lasts for 30 minutes automatically and then you can again place a request.
But you can Charge Water with energies and drink it whole day with VK
https://forum.litairian.com/discussion/1262/24-charging-water-things-methods#latest