"PlayStation users who currently have both a PS Now and PS Plus membership will be getting upgraded to the new PlayStation Plus Premium Tier when it launches this year. The length of the upgrade will be equal to the longest subscription owned.
[...]
So, for example, if you have PS Now subscribed up until August 2022 and an active PS Plus membership until September 2025 - that means you’ll be upgraded to PS Plus premium until September 2025 (or vice versa)."
Quelle: ign.com/articles/ps-plus-ps-no…r-dual-subscription-users