This is a Discord Snowflake Deconstructor. It takes a Discord Snowflake (Message ID) and shows you what time and day it was posted.
Every Discord message that is sent is attached with a message id, for developers and for refferal back the that message. This is called the Message ID.
To find any IDs, whether that be a User, Guild (server), Channel, VC (Voice Channel), Podcast and a lot more, you need to enable developer mode. In the following steps I will show you how to do this.
You should know how to get there. Desktop is in the bottom left of your screen, the little cog. iOS/Android is at the bottom bar cog.
It is the last in its category, under Streamer Mode.
Click the button on "Enable Developer Mode"
On Desktop, hover over the message you would like until you see the 3 dots on the mini-menu. On Mobile, click on the empty space of the message or on the message itself until the same appears.
Click the 3 dots on the menu, and then click copy id. It should now be copied to you clipboard, ready to paste!
Finally, go to the website and paste it into the input bar, and you should see the exact time and date the message was sent!