Can I park on a single yellow line outside the restricted hours in Northern Ireland?

Usually yes, once the signed restricted hours have ended, provided no other restriction applies.

Check for controlled parking zone signs, kerb blips, loading bans, clearway restrictions, permit bays and other road markings before leaving the vehicle.

For parking questions, the exact sign, road marking, kerb marking and hours of operation control the answer at the location. Photograph the signs and your vehicle position if there is any dispute, because a nearby restriction or controlled zone can change what would otherwise be allowed. For "Can I park on a single yellow line outside the restricted hours in Northern Ireland?", those details are especially important because the same road can have different rules by bay, side, time or vehicle class.