Direct Intervention or DI2 vs Veil of Darkness

Name: Veil of Darkness
[Gehenna:R]
Cardtype: Event
Gehenna. Do not replace as long as this card is in play.
Each turn, when a vampire plays his or her first card that turn that requires any Disciplines, that vampire's controller reveals the top card of his or her library (before drawing to replace). If it is a master card, the original card has no effect (no cost is paid), and in addition, if the original card required Obtenebration [obt], the vampire burns 2 blood.

Name: Direct Intervention
[Sabbat:U, SW:PB, Third:U, POD:DTC]
Cardtype: Master
Cost: 1 pool
Out-of-turn.
Cancel a minion card as it is played, and its cost is not paid. (If it was an action card, the acting minion does not lock. If it was a strike card, the minion chooses another strike.)
Artist: Harold Arthur McNeill; Ginés Quiñonero

When do I have to play a Direct Intervention to cancel a card requiring a disciplin? Before or after the revelation of the top card of the library?

May I wait if the card is canceled by drawing a master card and if it is not cancel it with my DI?

My take is you have to play DI before the check.