I generally rinse all my teas for about... perhaps 15 seconds? (I count [mutter] to 30 for about 2-3 long breaths).
The people I get my tea from (a local vendor), says that even if the tea is clean, the first brew typically contains all the caffeine, afterwards, the following brews contain no caffeine (and if there is any, I assume the amount is negligable).
I typically follow this rule even for teas from other vendors because a lot of vendors in my area advise to always rinse tea (I exclusively use loose leaf tea), because nearly all of the ones I used to frequent (I used to be a tea junkie, I've cooled down to being the occasional fan now
), actually owned the farms where they got the tea from and I assume since they've been in business for a long time despite the fact that a majority of their teas are expensive (in San Francisco, it's hard for a small business to survive if they aren't good).
I read somewhere that the rinse is like a wake up call to the tea (they start to open up), and then, the following infusions (typically an actual 30-60 seconds and range from 5-6 infusions) are the tea when the leaves actually starts unfurling and the taste is supposed to be better because the leaves are 'awake'.
Hopefully none of this sounds... off-putting, and it's not too much information (I ramble), it's just the way that I've been taught and I like to think of them as rules generally and in my case, it's not really too wasteful (I use a 8 oz. infuser and typically fill it to the brim to the case where water occasionally leaks out