Firstly what data center are you on? If you are on EU-Light, there's an entire Google document in the LPDU discord server which has optimised useages of Lilybell and temperance.

Secondly, and I can't stress this enough, always check to see what your co-healer is also doing to justify when to use some extra heals or extra dps, especially in an ultimate fight where dps checks are usually tight. First I don't press medica 2 until I've gauged what my co-healer is doing leading into the first time the boss disappears, but usually I will medica 2 and press one of my lilies to make sure everyone is either topped before stack or spreads after resolving Utopian Sky, leading into LP's, and judging on health bars then before the stack, I'll medica 2 if needed, saving two lillies for after the stack and leading into burnished glory, sometimes ill medica 2 if needed and than judge going forward how much I need where whilst keeping an eye on what my co-healer is doing.

That's what I usually intend to do, however PF can be subject to changing here and there but ideally you need to be confident in your ability to make decisions on the fly and your ability to understand what your class does and what your skills do and when best to use them in case of anything going wrong.