How long does a subscription to Twitch Prime last (via Amazon)?

I have a question about Twitch Prime,

I have it with Amazon Prime and normally you can (have to) use another streamer after 1 month. But e.g. At Monte it's like that, there are 2 monthly subs and such. How does it work or how does it work with Twitch Prime (Amazon)

So

if you have an amazonprime membership you have one free sub per month

why it is with monte 2 (if what you tell is true) could be because he is a twitch partner.

At Monte he always reads aloud… Has been there for 2 months

AHH that means he has been practicing for 2 months

either he just extended his sub (pay money) or extend it with twitch prime but I don't know