eVar expiry and First allocation

Hello,

I have a question about how custom time expiry works with first allocation. If I have eVar1 set to A on my first visit on Day 1, with 90 day expiry, and then I visit again and A is passed into eVar1 on Day 3. Would my first allocation expire on Day 91 or on Day 93? Basically, does the expiry start counting from the first time the particular value is set? Or does it start counting after the last time that the value was passed into the eVar?

Thanks