For me this question depends on wat boss fight. I sometimes end up waiting till the boss is in a good position or depending on wat time we genarally pop lust /heroism. Alot of time i pop em right away so they are up again later or the boss runs away at a certain point and comes back. Or say we lust at like 30% and i want my wings back up again. I pre haste pot so genarally popping them at the beginning is best for me.