
rechtzeitig
in time
Early enough or at the right moment, so that something is still possible or no disadvantage arises.
Wir müssen rechtzeitig losfahren, um den Zug nicht zu verpassen.
We have to leave in time so we don't miss the train.
in time / on time
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in time
Early enough or at the right moment, so that something is still possible or no disadvantage arises.
Wir müssen rechtzeitig losfahren, um den Zug nicht zu verpassen.
We have to leave in time so we don't miss the train.
The word is made up of 'recht' and 'zeitig'. Here, 'recht' means 'right' or 'appropriate'. So 'rechtzeitig' (in time) literally means 'at the right time'.
Danke für die rechtzeitige Warnung!
Thank you for the timely warning!
As an adverb, 'rechtzeitig' (in time) can stand in different positions in the sentence. It often stands directly before the verb or action it describes, or in position 1 for emphasis.
Wir haben das Problem noch rechtzeitig erkannt.
We recognized the problem just in time.
'Rechtzeitig' (in time) is often combined with verbs that involve an appointment or a deadline. Typical phrases are: 'rechtzeitig ankommen' (to arrive in time), 'rechtzeitig fertig werden' (to finish in time), or 'rechtzeitig Bescheid sagen' (to let someone know in time).
Bitte sag mir rechtzeitig Bescheid, ob du kommst.
Please let me know in time whether you're coming.
early
Früh means that someone arrives before the usual or expected time. Rechtzeitig only means that there is still enough time for the intended purpose. Someone who arrives früh is usually also rechtzeitig, but someone who arrives rechtzeitig does not have to arrive particularly early.

Wir kamen fünf Minuten vor der Abfahrt noch rechtzeitig am Bahnhof an.
We arrived at the station five minutes before departure, still in time.
Wir kamen schon eine Stunde vor der Abfahrt früh am Bahnhof an.
We arrived at the station early, a full hour before departure.