短短 + Time Expression + 内
短短 (duǎnduǎn) is the reduplicated form of 短 (short) and is used to emphasize that a period of time is surprisingly or notably brief. It is placed before a time expression to highlight how quickly something happened. For example, 短短两分钟内 means "in just two short minutes."
短短三个月,他的中文进步了这么多。
Duǎnduǎn sān gè yuè, tā de Zhōngwén jìnbù le zhème duō.
In just three months, his Chinese has improved so much.
短短几秒钟的时间,一切都变了。
Duǎnduǎn jǐ miǎozhōng de shíjiān, yíqiè dōu biàn le.
In just a few seconds, everything changed.
她在短短一年内就学会了做饭。
Tā zài duǎnduǎn yì nián nèi jiù xuéhuì le zuò fàn.
She learned to cook in just one year.