This feature allows user to temporary pin posts in the chat by replying with a /pin command to them.
Posts are pinned for 1 hour by default, but other durations could be provided, like /pin 2 hours 30 minutes.
Check out PinRequestFinder for the full list of the supported temporal units.
Pinning is charged with a special in-chat currency, named "pins". 1 pin allows to pin a post for one hour. Shorter durations are supported, but charged as a full hour. Pins are charged upfront when pinning a post.
Pins are not returned when a post is preemptively unpinned by an admin.