No, it is not safe. There are a lot of factors involved, including:

Is the 24VDc truly 24vdc,with no spikes, undershoots, etc ?

How fast is the transition from 0 to 24VDC ? Diodes can switch off quickly, but are not perfect devices. They have capacitance and a finite trr (reverse recovery time.)

Optos - generally a good idea to keep ground currents away from the 8052.

Without optos, you should use a buffer between +24 and the micro. An op-amp/ comparator would be ok, too.

You don't give enough information about the +24V signal - frequency, duty cycle, relation to 8052's power, etc.