Flyback Diode for 24V DC Solenoid
The switching time is not limited by the diode capacitance here but rather the flyback voltage and resistance time constant. 

The nature of solenoids are that they have very large inductance with very large forces in a small package and yet with 24V/8A=3 Ohms = DCR the release time constant is dictated by the Tau=L/R ratio. Thus a lower power dissipating low voltage diode is the slowest to dissipate the stored current.  

If speed and heat are to be optimized for the turnoff, you can use a small relay to switch the coil current and thus only have to deal with say a &lt;50mA drive current and use a shunt resistor to bypass some arc power to save the switching devices from stress.  e.g. V=Ldi/dt=IR

However dI/dt interference is expected when you increase the flyback voltage to speed up the de-activation, other methods can reduce these effects.

This device has a 2 second cycle time and low duty cycle, but you have not specified your requirements.