Since there’s a delay with Imps spawning and them actually attacking I decided to see if there are actual breakpoints for Imps attacking with the delay.
In testing found out the delay of Imp Spawn and the start of the first Fel Firebolt cast can vary anywhere between ~0.6s to ~1.6s sometimes lower sometimes higher, so I decided to just use an approximate value for the delay and gave it a 1s timer.
From there I calculated # of casts without Demonic Empowerment, # of casts with Demonic Empowerment and # of casts with Demonic Empowerment and Heroism/Lust.
In the spreadsheet you can change two values as needed;
May not end up being useful at all, but it did allow me to find out that your Imps are not locked by a GCD, so they can cast as fast as you have the haste for and depending on the delay you get between summon and first cast can get varied # of casts. That being said there are certain Haste values that could be used as ‘breakpoints’ because a partial cast is worth nothing. In the example at 35% Haste and 3/3 Summoner’s Prowess (56% Haste for DE) your imps average 11.58 casts per summon, so to min/max your haste you’d either round up or down;
40% Haste gives 12 casts with DE
28.25% Haste gives 11 casts with DE
Do with it as you will, might be useful in the long term for ultra min maxing.