Usamos ‘at’ para:

At + hora del día

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• At 6:30 - A las 6:30
• At 7 o'clock - A las siete
• At dawn - Al amanecer
• At lunchtime - Al mediodía
• At midnight - A la medianoche

At + día festivo

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• At Christmas - En Navidad
• At Easter - En Pascuas
• At New Year - En Año Nuevo
• At Lent - En Cuaresma
• At Holy Week - En Semana Santa

At + ciertas expresiones

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• At the moment - En este momento
• At the weekend - El fin de semana
• At that time - En ese tiempo
• At night - A la noche
• At noon - Al mediodía

Usamos ‘on’ para:

On + día

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• On Monday - El lunes
• On Tuesday - El martes
• On Wednesday - El miércoles
• On Thursday - El jueves

On + día + parte del día

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• On Friday morning - El viernes por la mañana
• On Saturday afternoon - El sábado por la tarde
• On Sunday evening - El domingo a la noche

On + fechas

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• On Christmas Day - El día de Navidad
• On July 4th - El 4 de Julio
• On December 31st 1966 - El 31 de diciembre de 1966

Usamos ‘in’ para:

In + partes del día

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• In the morning - Por la mañana
• In the afternoon - Por la tarde
• In the evening - Por la noche

In + meses

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• In January - En enero
• In February - En febrero
• In May - En mayo

In + años

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• In 1966 - En 1966
• In 1845 - En 1845
• In the 1960s - En los sesenta

In + estaciones del año

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• In summer - En verano
• In spring - En primavera
• In fall / autumn - En otoño
• In winter - En invierno
• In the early summer - El comenzar el verano

In + largos períodos

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• In the 19th century - En el siglo 19
• In the past - En el pasado
• In the future - En el futuro
• In the Middle Ages - En la Edad Media
• In the Stone Age - En la Edad de piedra

In + referencia al futuro

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• I will be there in two days - Estaré allí en dos días
• In nine months - En nueve meses
• In five minutes - En cinco minutos
• In three years - En tres años
• In seven hours - En siete horas