So what is the best time for lb in 4 ppl dungeon?Just got kicked becauz I refuse to lb at the beginning of boss fight.

Entered the Vault with another MCH dps new to the dungeon. I think the 2nd and final boss are ez to wipe without good positioning and healer. From the trash I can tell healer is OK but tank can not pick aggro very well. At the 2nd boss, Tank asked me to lb even before the boss turn to its true form I refused because I planned to lb when the fight becomes harder (when there more black holes). So our MCH lbed when the boss still got half HP. The result is MCH died and we almost wiped...Both healer and tank argued that when u used lb earlier, u got lb back earlier, but don't u always get almost full lb at the next boss?? Considering the difficulty of the fight, I argued that it's better to lb at end.
Then at the final boss I double-checked when they want me to lb. AND I GOT KICKED because of this question

So what is the best time for lb? Am I really wrong...