Time prepositions place events on the timeline and indicate start, duration, limit, frequency, or exact moment. They link the action to months, years, seasons, parts of the day, times and intervals, with values that depend on context and the preposition chosen. In Portuguese, this field includes simple forms such as Common prepositions and longer structures such as Prepositional phrases, always in relation to the verb and the temporal complement. The precise use of these forms helps organize the chronology of the sentence and to avoid ambiguities in speech and formal writing.

In introduces a broad temporal point, such as months, years, seasons and larger periods. It also appears with parts of the year and with names of periods that function as a temporal frame. This value is central to reading dates in Portuguese and is closely related to Time adverbs when the temporal expression acts as a circumstantial marker.

IdeiaIdea	ExemploExample
Em marca meses e anos.Marks months and years.	Em julho, viajamos.In July, we travel.
Em marca estações.Marks seasons.	Em verão, a cidade fica cheia.In summer, the city is crowded.
Em marca períodos amplos.Marks broad periods.	Em 1999, tudo era diferente.In 1999, everything was different.

No, na, nos and nas result from contracting in with a definite article and appear when the temporal complement requires an article. The form chosen agrees with the gender and number of the temporal noun, as in no verão, na primavera, nos fins de semana and nas férias. This contraction is mandatory in standard usage when the noun allows a definite article in that temporal value.

IdeiaIdea	ExemploExample
No aparece com nome masculino singular.No appears with masculine singular noun.	No verão, descanso mais.No verão, I rest more.
Na aparece com nome feminino singular.Na appears with feminine singular noun.	Na primavera, floresce tudo.Na primavera, everything blooms.
Nos e nas aparecem no plural.Nos and nas appear in the plural.	Nas férias, leio bastante.During the holidays, I read a lot.

For hours and time limits, the preposition 'a' is used, which normally contracts with the article and produces forms such as 'às'. This usage marks an instant, deadline or exact time range, such as 'às 15h', 'à meia-noite' or 'ao fim da tarde' when there is a time reference. The contraction follows the article's agreement with the temporal expression and is the expected form in formal writing.

IdeiaIdea	ExemploExample
Às marca hora exata no plural.The plural 'Às' marks the exact time (plural).	Às 15h, começa a reunião.At 3 PM, the meeting starts.
À marca hora singular feminina.The feminine singular form 'À' marks the time.	À meia noite, a rua fica silenciosa.At midnight, the street is quiet.
Ao marca referência horária masculina singular.The masculine singular reference 'Ao' marks the time reference.	Ao meio dia, paramos para almoçar.At noon, we stop to have lunch.

De can introduce parts of the day and temporal origins, such as de manhã, de tarde and 2010. Desde indica a starting point that continues to the present or until another reference moment, thus emphasizing continuity. The two forms are not interchangeable: de locates the temporal phase, while desde emphasizes continuous duration from a starting point.

IdeiaIdea	ExemploExample
De marca parte do dia.De marks part of the day.	De manhã, estudo melhor.In the morning, I study better.
De marca origem temporal.De marks temporal origin.	De 2010, moro aqui.Since 2010, I live here.
Desde marca continuidade.Desde marks continuity.	Desde 2015, trabalho nesta escola.Since 2015, I work at this school.

Until indicates the final limit of a temporal interval and shows where the action ends. It can combine with hours, dates, days or deadline expressions, such as until tomorrow, until 18:00 and until Sunday. The preposition fixes the end point and usually appears before the element that names the limit.

IdeiaIdea	ExemploExample
Até marca fim de prazo.Until marks the end of a deadline.	Entregue o relatório até amanhã.Deliver the report by tomorrow.
Até marca limite horário.Until marks the time limit.	Fico aqui até às 18h.I stay here until 18:00.
Até marca limite de data.Until marks the date limit.	A promoção vale até domingo.The promotion is valid until Sunday.

During indicates a continuous duration within a clearly delimited interval. For expresses approximate duration or a time extension not fully closed and also appears in fixed time expressions. The choice between the two depends on whether the speaker wants to emphasize internal continuity or just approximate duration of time.

IdeiaIdea	ExemploExample
Durante indica continuidade no intervalo.During indicates continuity within the interval.	Durante a noite, não dormi.During the night, I did not sleep.
Por indica duração aproximada.For indicates approximate duration.	Fiquei fora por duas semanas.I was away for two weeks.
Por aparece em locuções de tempo.For appears in time expressions.	Por enquanto, tudo bem.For now, everything is fine.

'Há' and 'faz' indicate elapsed time and respond to the idea of the past counted from the present. 'Há' is the most neutral and common form in formal writing, while 'faz' is more colloquial in many varieties of Portuguese. Both introduce the elapsed interval and require a stable temporal construction, such as 'há dois anos' and 'faz dois anos'.

IdeiaIdea	ExemploExample
Há marca tempo decorrido com registro neutro.Há marks elapsed time with a neutral tone.	Há dois anos, mudei de cidade.Two years ago, I moved to a city.
Faz marca tempo decorrido com tom mais coloquial.Faz marks elapsed time with a more colloquial tone.	Faz dois anos que mudei de cidade.It's been two years since I moved to the city.
Há também aparece em referência passada.Há also appears in past reference.	Há muito tempo, lia esse jornal.A long time ago, I read that newspaper.

'Before' and 'after' organize the temporal relationship between two events and show anteriority or posteriority. 'Between' can also place an event within the interval formed by two temporal markers, such as between January and March. These structures depend on the order of the events and help to make chronological sequences explicit.

IdeiaIdea	ExemploExample
Antes de indica anterioridade.Before indicates anteriority.	Antes de sair, feche a porta.Before leaving, close the door.
Depois de indica posterioridade.After indicates posteriority.	Depois de jantar, fomos caminhar.After dinner, we went for a walk.
Entre indica intervalo temporal.Between indicates a time interval.	Entre março e abril, choveu muito.Between March and April, it rained a lot.

Time prepositions organize chronology with complementary values: in situate broad periods; no and na adjust contraction with the article; the mark for hours and deadlines; de locates parts of the day; desde fixes the starting point; até delineates the end; during highlights continuity; por measures approximate duration; há and faz express elapsed time; and antes de, depois de and entre order events. Mastery of these relations improves temporal precision in Portuguese and facilitates natural choices in Verb tenses and in contexts of narration and exposition.