Do i need a short-time timer for coffee maker/water boiler?
If the appliances have their own timers built in, then I don't think an additional in line timer adds significant safety or energy efficiency. And given that any device can malfunction, any additional device can introduce risk. If you already have a built-in timer, then most of the time I would keep it in the indefinite on position if the other appliances have their own timers.

My sister has an electric hot water kettle which boils one quart to two quarts of water quickly and then keeps it near boiling. This is an energy efficient method for producing boiling water, but is an extra appliance cluttering the kitchen counter top.

I boil water on the kitchen stove and set the timer to alert me at a preset time. Sometimes I forget the kettle on the stove with the result that a lot of water vapor and heat is added to the air in the room.