die Stunde
hour
A unit of time that lasts 60 minutes.
Ich warte schon seit über einer Stunde auf den Bus.
I've been waiting for the bus for over an hour.

hour
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hour
A unit of time that lasts 60 minutes.
Ich warte schon seit über einer Stunde auf den Bus.
I've been waiting for the bus for over an hour.

'Stunde' (hour) is used with various prepositions for time expressions. 'In einer Stunde' describes a point in the future, 'vor einer Stunde' a point in the past, and 'seit einer Stunde' a duration that continues up to now.
Der Zug fährt in einer Stunde ab.
The train leaves in an hour.
In the context of school, university, or courses, 'Stunde' almost always means 'Unterrichtseinheit' (class/lesson) and not 60 minutes. Signal words are subjects like 'Mathe' (math), 'Deutsch' (German), or words like 'Lehrer' (teacher) and 'Unterricht' (instruction/class).
In der ersten Stunde haben wir heute Englisch.
In the first class today, we have English.
In this meaning, 'Stunde' is used in an elevated, often literary or emotional style to describe a decisive moment. Typical expressions are 'die Stunde der Wahrheit' (the moment of truth) or 'in der Stunde der Not' (in the hour of need).
In seiner schwersten Stunde waren seine Freunde für ihn da.
In his most difficult hour, his friends were there for him.
The expression 'zur Stunde' (at present) is a very formal way to say 'now' or 'currently'. You find it mainly in news reports, official announcements, or speeches.
Der Präsident ist zur Stunde nicht erreichbar.
The president is not reachable at present.
now
'jetzt' and 'zur Stunde' can both refer to the current moment. 'jetzt' is the normal everyday word. 'zur Stunde' is a fixed expression with 'die Stunde' and sounds more formal. You are more likely to hear it in news reports, reports, or official texts. What is important: 'die Stunde' by itself does not mean 'now'; the whole expression 'zur Stunde' does. In conversation, 'jetzt' is almost always more natural.

Zur Stunde liegen noch keine neuen Informationen vor.
At present, no new information is available yet.
Jetzt kann ich leider nicht telefonieren.
Unfortunately, I can't talk on the phone right now.