It's fine, you just need a few trials to figure out what happens at certain "cook" times with your specific microwave.
Black teas can often times be steeped as hot as you'd like, but you have to experiment with white and green teas in order to avoid the bitter taste since they're more delicate. It's usually safe to wait for thirty seconds to a minute before letting the green or white tea steep.
I don't remember the wattage of my microwave, but I find that half a mug of water for one tea bag of green tea takes well to 2 minutes and 15 seconds, while for a whole mug for two tea bags, I'll usually do about 2 minutes and 45 seconds.