EditPad Lite has a nice feature (CTRL-E, CTRL-I) which inserts a time stamp e.g. \"2008-09-11 10:34:53\" into your code.
To make it work cross-platform, just put the following in your vimrc:
nmap i=strftime("%Y-%m-%d %a %I:%M %p")
imap =strftime("%Y-%m-%d %a %I:%M %p")
Now you can just press F3 any time inside Vi/Vim and you'll get a timestamp like 2016-01-25 Mo 12:44 inserted at the cursor.
For a complete description of the available parameters check the documentation of the C function strftime().