DASH InstantSend (formerly InstantX)

DASH offers an "instant" transaction method known as InstantSend.

To take advantage of InstantSend withdrawals on Kraken, a withdrawal address must first be whitelisted on your account. The first successful withdrawal to an DASH address whitelists it for future, faster transactions under InstantSend.

Note: if the destination doesn’t recognize InstantSend payments, transactions may take another 10-15 minutes.

For more information on DASH InstantSend, see: 
https://docs.dash.org/en/latest/introduction/features.html#instantsend