Due to arrive
"What time is he due to arrive'"
I have seen this translated as "¿A qué hora llega (o, va a llegar)'," but this translation loses the nuance of expectation. That is, "due to" here means the time when he is expected to arrive, which may or may not be the time when he actually does arrive. We use this for trains, planes, buses, and other things that arrive on a schedule. We also use it for anything that can occur on a schedule.
I understand that the most natural thing for a Spanish speaker to say in this situation is probably just what I gave above, but is there a good way to include the nuance I mentioned'
Did you mean to say horas in plural'
May be ¿A qué hora se espera su llegada? or ¿A qué hora debería llegar'.
Although, the most natural form is that you have shown.