Hello. As the Premium system is now with a specific chapter unlocking with each "time based" unlock (calling it a "Time Unlock" from now on) regardless of if a reader has unlocked it with spirit stones or not it actually discourages using spirit stones (and by extension discourages buying extra SS). The problem is that if you unlock premium chapters you either have to keep unlocking chapters or wait at least as many days as chapters you unlocked before the free chapters "Catch up". This might not be much of an issue when you unlock one or two but unlocking several chapters can mean a wait of weeks or for those like Immortal mortal with 170+ premium chapters a wait of several months if you unlock all current chapters in one go which might cause people to forget the story and not resume reading it later.
If the system is changed to an individual one however so that every time the "Time Unlock" occurs it automatically unlocks the next locked chapter for every individual reader, then there is no reason not to use SS to unlock premium chapters (other than the amount of SS it costs of course) and it removes the one (big) drawback of buying extra ss.
A variation the company might prefer is if the premium chapters are divided into two types, one "Hard-Locked" and one "Soft-Locked" where the "Hard-Locked" chapters can only be unlocked with SS even if a "Time Unlock" occurs and they turn into "Soft-Locked" after either a duration (like a week) or after a certain amount of new chapters are released (about an average weeks worth). The "Soft-Locked" chapters can be unlocked with SS like the "Hard-Locked ones but are also eligible for the "Timed Unlock". Basically the "Timed Unlock" unlocks the next available "Soft-Locked" chapter for a reader. This makes it so that if you have read up to the latest chapter but can't afford enough SS to keep up with the latest chapter released or want to use your SS on another novel you only have to wait for maybe a week before you start getting free chapters for the first novel again, then you can either keep reading at the speed of "Time Unlocks", use some a mix of SS and the "Time Unlocks" and keep reading at the release speed (but a week or so behind the newest chapter) or use SS to catch up to the newest chapter again when you can afford the SS (or regain interest in the story/hit an extra "cliffy" cliffhanger)
The "Buffer" of "Hard-Locked" chapters shouldn't exceed a week (or two at most) since that just increases the risk of people forgetting/dropping the novel if they can't keep up with spending SS.
The "Soft-Locked" chapters should be marked some way so you can see that they are eligible for the "Time Unlocks" and might be nice if the last "Soft-Locked" chapter before the buffer of "Hard-locked" ones is marked in a special way so that you don't "accidentaly" unlock it for SS and miss a "Time Unlock"
Having the Individual system (with or without the buffer of "Hard-locked" chapters) is a lot more reader friendly since you can read ahead (for a cost of SS (both bought and bonus ones)) without being punished for it (forced to decide between waiting for the free chapter to catch up or keep spending SS). Also since there isn't a drawback other than cost (which can feel a bit insane per chapter especially if you might feel "forced" to pay it like now) more people will probably be willing to buy SS to unlock a chunk of chapters at a time.
Just my thoughts on how to improve the premium system.
