Instant coffee!!!?? aruuugh - I'd slap that cup right out of your hand. Such evil stuff that is - so sooooo so evil.
I don't know what temperature we're brewing our chamomile at - we boil the jug, give it a minute to take the worst of the heat off, pour it into the teapot... and wait.
The 20~25 minute thing has come about after a year or so of trying - we sort of came to liking it by accident when we forgot the pot one day. Since then that's how we've found we prefer it.
Paul.