中文：

最早什么时候可以挂单？

在股票交易中，挂单指的是投资者在交易平台中提交的购买或卖出订单。这个订单通常会立即被交易所处理，或者在特定时间段内被处理。那么，最早什么时候可以挂单呢？

一般来说，最早可以在前一天晚上的九点左右开始挂单。因为交易所通常会在次日早上九点左右开始接受订单，这个时间点前提交的订单都会在当天的交易中得到处理。但是需要注意的是，不同的交易所可能有不同的规定，投资者应该根据自己所在的交易所的规定来确定最早的挂单时间。

另外，如果是进行夜市交易的投资者，则需要在晚上的七点左右开始挂单。因为夜市交易的时间是在晚上七点到次日凌晨五点左右。在这个时间段内提交的订单也会在次日的交易中得到处理。

总的来说，最早什么时候可以挂单取决于所在的交易所的规定以及交易的时间段。投资者应该根据自己的情况选择合适的时间点进行挂单，以获得更好的交易效果。

英文：

When can the earliest挂单?

In stock trading, hanging order refers to the purchase or sale order submitted by investors on the trading platform. This order is usually processed immediately by the exchange or processed within a specific time period. So, when can the earliest hanging order be placed?

Generally speaking, the earliest hanging order can be started at about 9 o'clock in the evening of the previous day. Because the exchange usually starts accepting orders at about 9 o'clock in the morning of the next day, orders submitted before this time will be processed in the same day's trading. However, it should be noted that different exchanges may have different regulations, so investors should determine the earliest hanging order time based on the regulations of their respective exchanges.

In addition, if investors want to trade at night, they need to start hanging orders at about 7 o'clock in the evening. Because night trading time is from 7 pm to 5 am the next day. Orders submitted during this time will also be processed in the next day's trading.

Overall, when can the earliest hanging order depends on the regulations of the exchange and the trading time period. Investors should choose the appropriate time point for hanging orders according to their own situation to obtain better trading results.