I have added this request and we should be able to add it to a future version. Thanks!

我已经提交了这项请求，我们应该能够在未来的版本中添加它。谢谢！

Sorry, I was mistaken and we have already added this into the current public version! If you right-click on the taskbar you want to show seconds on, then click Multi-Monitor Taskbar > System Tray Clock > Show Seconds. I hope this helps!