From original project wiki:

delay:: Amount of time (in milliseconds) that the player must wait after completing this Stage, before the Quest will advance to the next one
(Optional) delay-message: Message sent to the player when the delay begins 

There are 2 bugs:

• delay are seems to be actually counted in minutes
• delay-message is sent after delay ends

In my server it seems to be in seconds :/

This is official wiki: https://github.com/FlyingPikachu/Quests/wiki

The delay is in seconds as of Quests 2.3.4. I believe the delay-message behavior is intentional despite the original wiki. If you have more reason to believe otherwise, please open a new ticket.

I will test more about the delay.
But I guess there is no doc about delay-message