Could I say at one o/clock “Il arrive d’ici deux heures” to mean he is arriving at 2 o/clock?

That would mean that he will be coming within two hours. If you want to say that he is arriving at 2 o'clock, you'd say, "Il arrive à deux heures."

According to the lesson, the à is not necessary.

But also :

If you want to say "he arrives at 2 0'clock" the à is required.

Il arrive à deux heures. -- He arrives at 2 o'clock.
Il arrive d'ici deux heures. -- He arrives by 2 o'clock.