Instead,slow earthquakes release their energy over a period of hours or even days.

VOA: special.2009.07.07

So it's important to be here on time and stay throughout 3 hours' period.

一定不能迟到,每节课3个小时，不能早退。

麻省理工公开课 - 电影哲学课程节选

During the summer, the most dangerous period for U-V rays in the United States mainland is between the hours of ten in the morning and four in the afternoon.

VOA: special.2010.07.06

This is expected very soon in Cairo." The coming 72 hours,argues Saif, is a very critical period, as both parties jockey for position and fighting intensifies.

VOA: standard.2009.10.11