Rectangle time is the time of day when people in an obviously social setting instead choose to pull out their smart phones and have some time alone with their "rectangle". The term can also apply to other electronics, such as computers, iPads, etc.

“矩形时间”指人们在社交场合选择拿出智能手机，和自己的“矩形”独处的时间。“矩形时间”这一短语也可以应用于其他电子产品，如电脑、iPad等。

Example:

"Having some rectangle time there, I see," she said to Luke, as he stared at the phone screen while sitting on a scenic beach.

“原来是在享受‘矩形时间’啊，”她对坐在风光优美的海滩上盯着手机屏幕的卢克说道。