＞ When does the Unity Runtime Fee take effect?

（略）

    For existing customers renewing their paid Unity subscription plan between now and Dec 31, 2023, the policy will apply upon renewal and the fee will take effect, if applicable, on January 1, 2024.
    For existing customers renewing their paid plan in 2024 and beyond, the fee will take effect on January 1, 2024 or, in some cases, on the first of the month after the subscription end date.

と言う1項目がある。

https://unity.com/pricing-updates?utm_source=twitter&utm_medium=social&utm_campaign=company_global_blog_2023-09-12_faq