die Dauer
duration
The period of time for which something lasts or continues.
Die genaue Dauer der Reparatur ist noch nicht bekannt.
The exact duration of the repair is not yet known.

duration
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duration
The period of time for which something lasts or continues.
Die genaue Dauer der Reparatur ist noch nicht bekannt.
The exact duration of the repair is not yet known.

'Die Dauer' (duration) is the noun related to the verb 'dauern' (to last). If something 'dauert' (lasts) for a certain time, then that span of time is 'die Dauer' (the duration).
Der Film dauert zwei Stunden. Die Dauer beträgt also zwei Stunden.
The film lasts two hours. So the duration is two hours.
To name a concrete span of time, the preposition 'von' (of) is often used. Another typical phrase is 'von kurzer/langer Dauer sein' (to be of short/long duration).
Die Besprechung hatte eine Dauer von nur 30 Minuten.
The meeting had a duration of only 30 minutes.
The expression 'auf die Dauer' (in the long run) is a fixed phrase and means 'langfristig' (long-term) or 'über eine längere Zeit gesehen' (seen over a longer period of time). It is used to talk about long-term consequences or conditions.
Täglicher Stress ist auf die Dauer nicht gesund.
Daily stress is not healthy in the long run.
time
'die Zeit' and 'die Dauer' can both talk about a period during which something happens. However, 'die Zeit' is much more general and can mean a period, an era, or available time. 'die Dauer' asks more precisely how long something lasts. Learners confuse the words because in both cases you think of minutes, hours, or days. If you mean the length of an activity, 'die Dauer' is more precise. If you are talking generally about a period of time, 'die Zeit' sounds more natural.

Die Dauer der Prüfung steht auf dem ersten Blatt.
The duration of the exam is written on the first sheet.
Im Kurs haben wir heute viel Zeit mit Gruppenarbeit verbracht.
In the course today, we spent a lot of time on group work.