Does Arcane Surge buff affect the same cast of spell it activated from?

I always thought that if a cast of spell activates Arcane Surge it itself gains the buff.

But do we have confirmation from devs? There's nothing in the wiki.

Do you guys have any info about it?

Like, for example, if I cast Fireball that activates Arcane Surge, there's a time lag between end of cast and ball of fire hitting a mob.

Obviously when it hits Arcane Surge is already active.

But what about spells which hit right at the end of the cast?

Like Cold Snap for example. There's no time lag between end of the cast and spell hitting.

Does Arcane Surge affect that first cast it activated from?

What about Frostblink which is instant??