I designed those spells. Since all other spells take effect the moment that they're cast, I would say that the nebula starts attacking at once.
A follow up question if you don't mind.
The roots Mörk nebulosa från Alrechalir (page 48), and Mörk nebulosa från Razalgenar (page 49) have a similar text regarding the way they attack and you defend against it that I quite don't understand.
Mörk nebulosa från Alrechalir
Svårigheten att undkomma dess attacker är 12 och den orsakar Lamslagen (1T6 rundor) och sedan Fallskada 3T6 mot varelser som blivit lamslagna. Försvar kan göras med Förvränga, Undvika eller Självkontroll (endast mot Lamslagen).
which I have translated as
The difficulty to avoid its attacks is 12 and it inflicts Frozen (1d6 rounds) and then deals 3d6 Fall Damage against creatures that have been frozen. Defenses can be made with Disrupt, Dodge, or Discipline (only against Frozen).
What does it mean that you can only use Discipline against Frozen? does this mean that you also roll to defend against the Fall Damage? is it a separate attack? When does the Fall Damage attack happen? After the 1d6 rounds of Frozen are over? or right the next turn once Frozen is inflcited?
Similarly
Mörk nebulosa från Razalgenar
Svårigheten att undkomma dess attacker är 12 och den orsakar först Vildsint anfall (1T6 rundor), och därefter Eterskada 3T6 mot individer som drabbats av detta och utsiktslöst försöker angripa den. Försvar kan göras med Förvränga, Undvika eller Självkontroll (endast mot Vildsint anfall).
which I have translated as
The difficulty to avoid its attacks is 12 and it first inflicts Wild Attack (1d6 rounds), and then deals 3d6 Ether damage (acts as Burn damage) to individuals affected by it and hopelessly attempting to attack it. Defense can be done with Disrupt, Dodge, or Discipline (against Wild Attack only).
I have the same doubts in this case. What does it mean that you can only use Discipline against Wild attack? does this mean that you also roll to defend against the Ether Damage? is it a separate attack? When does the ether Damage attack happen? After the 1d6 rounds of Wild attack are over? or right the next turn once wild attack is inflcited?
Thanks for your patience.