heavy date并不是“沉重的约会”，而是表达“重要的约会”，或者“与异性的幽会”。

a planned meeting between two people who are very interested in having a romantic or sexual relationship

例句：

I think Carol has a heavy date - she's been in the bathroom for over an hour.

我想卡罗尔有个重要的约会——她已经在浴室里呆了一个多小时了。