I guess it depends on the context but most of the time: "late" would be "en retard" "early" would be "en avance"

late it's retard with frensh language EX: le professeur arrive tard à l'école/Professor arrives late to school early: le professeur vient à l'école tôt / teacher comes to school early

More examples that may be helpful! I know you meant early as an adverb but some of the examples here use 'early' as an adjective. tôt dans l'après-midi = early in the afternoon, in the early afternoon j'ai l'habitude de me coucher tôt = I normally ou usually go to bed early de bon ou grand matin = in the early morning, early in the morning en début/fin d'après-midi = early/late in the afternoon partir au petit matin = to leave early in the morning rentrer au petit matin = to come home in the early ou small hours

Also: 'de bonne heure' means early: Il faut que j'arrive de bonne heure. This has the sense of 'in plenty of time'