How to use the online timer
Three minutes suits most black tea steeped in water just off the boil, which is the timing that gets a decent cup without tipping into the bitterness that comes from over-steeping — that bitter edge is tannins doing exactly what they're meant to do, just for longer than most people actually want. Green and white teas want considerably less time and a cooler water temperature, since boiling water scalds the more delicate leaves and turns them grassy or bitter almost immediately.
Water temperature matters as much as the timer for anything other than black tea. Water straight off a rolling boil suits black tea and most herbal blends, but green tea prefers water that's been left to cool for a minute or two first, and delicate white teas cooler again.
Once the timer's done, pull the bag or leaves out rather than leaving them to keep steeping in the cup — this is the single biggest difference between a cup that tastes balanced and one that tastes stewed. If you like your tea stronger, use more leaf or a bigger bag rather than steeping for longer, since extra time mostly adds bitterness rather than flavour.
Common questions
Why does my tea taste bitter even at three minutes?
Water that's too hot for the tea type, or leaves left in the cup after steeping, are the usual causes. Remove the bag or leaves the moment the timer ends.
Can I just steep longer to get a stronger cup?
Not really — extra time mostly extracts more tannins, which reads as bitterness rather than strength. Use more tea leaf instead if you want a bolder cup.