Using connected PC keyboard input for VHDL Simulation
The simulation is not running at real-time speed, so even if you could use the keyboard as an input to the simulation you would not be able to reliably determine how long a key was pressed.

You need to create a testbench for your project, and simulate a key press in the testbench. This will allow you to precisely control the length of the key press signal while observing all of the important signals inside your design.