Modifier + 时期
The noun 时期 (shíqī) means 'period' or 'era' and is used to refer to a span of time characterized by particular events or conditions. It is commonly modified by adjectives or other nouns, as in 战争时期 (wartime period) or 历史时期 (historical period).
那是一段很困难的时期。
Nà shì yí duàn hěn kùnnán de shíqī.
That was a very difficult period.
大学时期是我最开心的日子。
Dàxué shíqī shì wǒ zuì kāixīn de rìzi.
My college years were my happiest days.
战争时期很多人离开了家乡。
Zhànzhēng shíqī hěn duō rén líkāi le jiāxiāng.
During wartime, many people left their hometowns.