That doesn't solve the problem at all. It's just a timer, but the user's inhalation force still dictates how much of the drug is consumed during that time.

Vape cartridges are nowhere near precise enough for normal drug delivery, even with a timer attached. It's just not a precision dosing method. Remember that pharmaceutical users wouldn't have any baseline to work with, whereas vape pen users have calibrated themselves over many doses across many sessions.