Basic Understanding of uncertainity principle

Take a box equipped with a shutter and a clock.The box is lined with perfectly reflecting mirrors and contains photons.The clock is very accurate and acts as a timer.Precisely at a certain time 't1' the shutter opens releasing one photon.The shutter is closed at time't2'.By making the interval 't2-t1' as small as possible we will know with high accuracy,the time when the photon escaped.therefore the error in 't' can be made as small as we please.the energy of the photon can also be accurately determined by subtracting the final weight of the box from the initial weight,and finding the energy by the mass-energy equation.Or the error in energy and time can be made as small as possible,which is a violation of the uncertainity principle!Is this argument valid?If no why?