Hurry! The train leaves _________ five minutes.

• Correct sentence - 
Hurry! The train leaves in five minutes.

Preposition এর ক্ষেত্রে,
Period of time - 
কিন্তু period of time (গণনাযোগ্য সময়) এর ক্ষেত্রে in হয়।
Hurry! The train leaves in five minutes.
Hurry up! We have to go in five minutes.
The film will start in fifteen minutes.
I will be back in an hour.
I will finish the job in two days/weeks/months.

• Point of time - 
নির্দিষ্ট মুহূর্ত, অগণনাযোগ্য সময় এর ক্ষেত্রে by হয়।
We have to go by 5 p.m./a.m./o'clock.
I will be back by five o'clock.
I have to finish it by Friday.
I will see by 21 instant.