While you are using any other apps, to create a date-and-time stamp,
1. just go the Notification Drawer, and tap the AutoHongKong notification. Then, this app will create a data-and-time stamp in the clipboard and return to the original app you have been using.
2. So you will be able to paste the date-and-time stamp in that app in this format:
2014-05-21 06:03:14 PM
Simplicity is the strength of this app, but in case you want to customize the date and time stamp format, please consider to buy my another app "Bubble Date Stamp & Time Stamp" instead.