Hmm... have you tried messing around with the EffectDelay tag (maybe a negative number)? It's an outside shot, but the only thing that comes to mind.

Honestly, most of my own effects last a few seconds at the most.

Have you tried adding in the code for projectile effects with an invisible projectile animation? If you set the speed low enough, and there is a way to get the effect bound to the target to play before the projectile 'hits,' you might be able to get what you're looking for. If that doesn't work, it's probably hard-coded.

Also, slightly off-topic, I'm kind of curious as to what you've come up with as far as custom spells go. Sharing is caring!

It's nice how the dragon politely waits for the cute fireworks to finish, not biting his head off at all

However, I can imagine the player to become a bit impatient after seeing this for the tenth time.

I had a chat with Cari_Elf and unfortunately the solution involves creating a unique bones animation. Since the animations are only indirectly tied to the spells, it is not possible to give this delay to any unit with more than one spell. If anyone googles in the future and finds this topic, you can find an example of the "effectdetach" if you study D_Dragon_Attack_02.hkb animation for dragonfire attacks.