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Catching a flyback pulse is actually a rather easy application for a diode.  Many of the diode parameters don't matter much.  The basics are:<ol>

<p><li>Reverse voltage.  This is simply the maximum voltage the coil will be driven with, which is 24 V in your example.  There is nothing magic about the flyback catching role here.

<p><li>Forward current capability.  This is just the maximum current there will ever be in the coil when it is suddenly turned off.  Your relay coil dissipates 700 mW with 24 V across it.  (700 mW)/(24 V) = 30 mA.  The current can't somehow magically be higher than that.

</ol>

Note that for a relay that isn't regularly pulsed, you can use the maximum pulse current spec for the diode instead of the continuous current spec.  Every time the relay is switched off, there is a finite amount of energy that will be dissipated by the diode.  At most, the diode will dissipate only the energy stored in the coil.  In practice, the coil resistance actually dissipates most of that energy.

One spec you didn't mention that sometimes does matter for flyback-catching applications is <i>reverse recovery time</i>.  That is important when the coil may be switched on again before the current from the previous pulse has fully died down yet.  This is common in PWM applications.  In such cases, during the time the diode is still on but the new pulse has already started, the diode becomes a short across the coil.  This can damage the diode, damage the switch, and/or draw too much supply current.  At the low voltages in your example, a Schottky diode would be an obvious solution to this.