I'm not sure if the new Seraphs is actually good on Sona - it might be, it might not be (I will say the shield feels fat). Imo it takes actually playing the game to get a feel for these things. But one thing you can look at the wiki for is how long it takes to stack your tear (and knowing that might help you faster get a feel for it or when you can buy it).

Tear gives 3 mana per spell, 6 if on a champion, and if you stack it perfectly consistently that's every 8 seconds. So to get to 360 bonus mana, 360/6 = 60 charges, 60 charges * 8 charges per sec = 480s, or 8 minutes.

A conversation with chat gpt:

me how long does it take to stack tear fully in league of legends

gpt The amount of time it takes to fully stack Tear of the Goddess in League of Legends can vary depending on a few factors, such as the champion being played and the playstyle of the player. Typically, it can take around 10-15 minutes to fully stack Tear of the Goddess if the player is consistently using their abilities and last hitting minions.

me How many seconds does it take to stack tear fully in league, assuming you use an ability on a champion every time you have a tear stack up

gpt The Tear of the Goddess item in League of Legends grants 1 stack of mana each time an ability is used, and it can hold up to 750 stacks, so it would take 750 ability uses to fully stack the item. The time it would take to fully stack the item would depend on how quickly the player is able to use their abilities and how often they are in a position to use them.

gpt Assuming a player is able to use their abilities every 2 seconds, it would take them around 15 minutes (750 x 2 = 1500 seconds) to fully stack Tear of the Goddess. However, this is a purely hypothetical scenario and in a real game, it would depend on many factors and could vary greatly.

me Tear can be stacked up to 360 mana, each stack gives 6 mana, if you get a stack every 8 seconds how long does it take to fully stack?

gpt Tear of the Goddess can be stacked up to 360 mana, and each stack gives 6 mana, so it would take 60 stacks to fully stack the item.

gpt If a player is able to gain a stack every 8 seconds, it would take them 480 seconds or 8 minutes to fully stack Tear of the Goddess.

gpt Please note that this is a hypothetical scenario and in a real game, the time it would take to fully stack Tear of the Goddess would depend on many factors such as the player's ability to use their abilities, the situation of the game, etc.

It doesn't have recent info, like the latest league of legends patch notes, so clearly it's useless. But actually pretty impressive even though you have to spoonfeed it a little with the prompt.

Also:

me should I buy tear on sona

gpt Whether or not to buy Tear of the Goddess on Sona in League of Legends depends on your playstyle and the current state of the game.

Tear of the Goddess is a useful item for Sona because it increases her mana pool and allows her to use her abilities more frequently. This can be especially helpful in the early game when Sona's mana pool is relatively small.

However, Tear of the Goddess is not an essential item for Sona and there are other items that can also be beneficial for her, such as Morellonomicon, which grants additional ability power, and a reduced cooldown on Sona's abilities. The choice of items will depend on how you want to play Sona, and what are the needs of the game.

It is always recommended to adapt to the game and consider the enemy team composition and your allies as well.

(me again)

so....it's cool but eh kinda just states relevant facts and irrelevant platitudes (not unlike many people who talk about league in that way though), in some ways "Whether or not to buy Tear of the Goddess on Sona in League of Legends depends on your playstyle and the current state of the game." is the perfect example of advice I don't like - it sounds good but doesn't really help because it isn't based on seeing what's strong in the game

I suppose the waffling on how it's typically 10-15 minutes in real games is good and important though