allmählich
gradually
Happening slowly and step by step over a longer period of time.
Allmählich wurde es dunkel und die Sterne kamen zum Vorschein.
Gradually it got dark and the stars appeared.

gradually
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gradually
Happening slowly and step by step over a longer period of time.
Allmählich wurde es dunkel und die Sterne kamen zum Vorschein.
Gradually it got dark and the stars appeared.

As an adverb, 'allmählich' (gradually) can stand flexibly in the sentence. If it stands at the beginning in position 1, the verb follows directly. But it can also stand after the verb and subject.
Allmählich verstand ich das Problem.
Gradually, I understood the problem.
'Allmählich' (gradually) describes a slow change and is therefore often combined with verbs of change. Typical examples are 'allmählich werden' (to gradually become), 'beginnen' (to begin), 'sich gewöhnen' (to get used to), or 'verstehen' (to understand).
Die Kinder gewöhnen sich allmählich an die neue Schule.
The children are gradually getting used to the new school.
The word emphasizes a process that does not happen suddenly, but in small, barely noticeable steps. It often describes natural developments or slow changes.
Nach dem langen Winter wird es allmählich wärmer.
After the long winter, it is gradually getting warmer.
time
'mit der Zeit' (over time) and 'allmählich' both describe that something does not happen immediately, but slowly, step by step. 'mit der Zeit' emphasizes the process over a longer period of time. 'allmählich' describes the slow change itself more directly. Often you can use both in similar ways, for example with habits, feelings, or improvements. 'mit der Zeit' sounds a bit more like a development over a longer time, while 'allmählich' fits well when you want to emphasize the slow process in the sentence.

Nach dem Training wird ihr Rücken allmählich stärker.
After the training, her back is gradually getting stronger.
Mit der Zeit wird er bei der Arbeit sicherer.
Over time, he will become more confident at work.