You can use bloodlust in 3 spots:
A) phase 1 to skip second add
B) beginning of phase 2 to shorten the phase and skip the not-soaked harvest into storm combo
C) phase 2 on 15% to make the push to 0% before phase 3 starts
Just forget about option C. you don't need it. you likely don't even need dps potions and/or cooldowns if you have 20 alive. We used 2 tanks/4 healers and used nothing and made that push. Our raid's dps is okay but nothing to get excited about. if you have problems, just use the second potion here. don't keep lust for this.
B) certainly works but most guilds that do that still push phase 1 before the second add. that's typically nothing you do on your first kill. it's overall probably the best and most efficient way as it means you can kill the boss in 10 minutes as you don't have to hold dps during the storm/harvest combo.
A) is what I strongly suggest to anyone working on Guldan right now. Phase 1 is a lot about people learning correct movement and maximizing their dps. Just use lust and zerg it. Note that bloodlust and the encounter haste buff stack but they don't stack all that well as the encounter buff reduces uptime on cooldowns and bloodlust itself:
https://www.warcraftlogs.com/reports...6&ability=2825