This is one of those art over science topics for me. It’s likely not something measurable, so you can only go on experience.

I’ve experienced break/burn-in twice where I genuinely noticed something. The first was with new tubes in an integrated amp - a harshness/hardness in the top end softened and became more sweet. The second, when upgrading from Klipsch Forte III to Cornwall IV. Initially the Cornwall bass sounded very thin but filled out after a few hours.

Either way, if it sounds good that’s all that matters.