The phrase “à quelle heure” literally means, “at what time”, but we don’t always use the word “at” in English.

At what time is the reservation?
What time is the reservation?

At what time does the film start?
What time does the film start?

At what time is dinner?
What time is dinner?

In English, occasionally, you’ll hear people even put the word “at” at the end of the question:

What time is dinner at?

In French, however, you always say, “à quelle heure”, and never just “quelle heure”

À quelle heure est la reservation? – (At) what time is the reservation?
À quelle heure le film commence-t-il? – (At) what time does the film start?
À quelle heure est le dîner? – (At) what time is dinner?

I just said that you never use “quelle heure” instead of “à quelle heure”, however, there is one time when you do. If you’re asking, “What time is it?”, meaning, “What is the time right now?”, you use this question:

Quelle heure est-il? – What time is it (right now)?