If you're biding your time, you're waiting for something.
To bide means to stay put and wait. If you finish a test first, you may have to bide your time until everyone else is done and you can leave class. Nowadays, the old-fashioned word bide is almost always paired with time. If you're biding your time, it's like you're treading water or in a holding pattern.
Here are some examples of biding time used correctly:
Bryant is biding his time, waiting for his chance to return to the starting lineup and again become a force in the post. (Washington Post)
They bide their time playing soccer and keep warm by building small fires. (Seattle Times)
Since bide is an unusual word that shows up almost exclusively in biding time, people sometimes think the expression is biting time. The word bite is a lot more common than bide. Plus, biding and biting sound about the same when you say them out loud. Maybe people imagine biting time to be chomping on a clock — but that strange image doesn't quite convey the sense of waiting patiently.
At a restaurant, you might bide your time reading and rereading a menu while you wait for the server, but make sure you're just biding your time and leave the biting for the food.