I'm expecting the answer to this question is probably "can't be done":

Is it possible to create a hallucination or broodling that starts with less than 180 on it's spawn timer? Or alternatively increase the speed at which the spawn timer depletes?

You could kill the hallucination faster through triggers, but I don't think there's any direct way to kill the hallucinated unit faster by altering it's energy.

Correct. Can't be done. Creating broodlings with properties (or was it without?) removes the timer entirely but that's all you can do to influence the timer.

A possible workaround would be to have them followed by a 1x1 pixel location and kill it after a certain period. Or just spawn it with low hp, so it dies earlier in battle, if that's an option.

Yeah, that's about what I thought. I want to stray away from arbitrarily killing the unit after an amount of time as it's not clear to the player why it died (without giving them some kind of message).

As for spawning a broodling with the timer, it seems creating it with properties will do that, regular creation does not.

Has anyone played around with that secondary HP box in scmdraft for the broodling? Perhaps that could have an influence on it's timer? I'm at work so can't test it myself.

The secondary hp box just makes the units current hp 1 more than its max. It doesn't matter what you put in the box though, as long as it's not 0. For example, a zergling has 35 max life. Put a number, say 4, in the small box. Then in game, the ling will have 36/35 life, making it's unit wireframe all funky.

the secondary hp box is the 1st byte of hp, which is used when healing units via medic, scv, or regeneration by adding a small amount to it each frame. Once it hits 256, it will roll over to 1 normal hp.

HP is a 4 byte value, but the first byte is hidden, and generally ignored. The number can be any number from 0-255, but SCMDraft only allows 1 digit in the box.

Right, I thought it was used for something like that.

So if scmdraft let you set that value to say 250, would that mean your unit would heal really quickly (if were zerg), because that value would go from 250-256 really fast and start back again at 250?

It doesn't edit healing speed, so no.

Zerg regenerates at 4 per frame. Shields regenerate at 7 per frame. Energy regenerates at 8 per frame. You can't change these without modding.

Essentially HP is 4 bytes:
00 64 00 00
Would be a 100 HP unit. That's how it looks in SC's memory. The first byte is the least significant, with the 4th byte being the 2^24th place. Normally HP can't go over 9999, so you'd never actually use that 4th byte. If it's confusing, blame intel for little endian notation.

If you set this 100 HP unit to have a 9 in the box, it would look like this:
09 64 00 00
Since the unit has 100.035 life, it rounds up to 101 in the GUI, but it still has 100.035 hp. It's not really that important, but when a unit does .5 damage to a unit, it actually subtracts 128 from the first byte (which is half an hp). When a concussive unit damages a large unit, often times it will do some fraction of damage. This isn't lost, and 4 hits on a large unit will actually do the full listed damage, since concussive does 25% to large.

In short, the first byte really does matter, but it's hidden away where we can't even edit it, or see it without using a hex editor or (maybe) starforge.

Hallucinations can take damage, yes?

If you can afford to track the hallucination at all, you can try using DDS (Direct Damage System) on it. The fact that you can't detect it in conditions, however, may complicate things. (But then, I've no idea how DDS works, TBH. It just sounds like a decent idea here)