setting screenshots location:

  1. open terminal
  2. create a folder for your new screenshots location 
    mkdir /users/myusername/Desktop/Screenshots
  3. set new location 
    defaults write com.apple.screencapture location /users/myusername/Desktop/Screenshots
  4. reset mac UI 
    killall SystemUIServer

changing timestamp format to 24h (DD:MM:YYYY HH:MM:SS) 

1. System Preferences
2. Language & Region
3. click Advanced...
4. choose the Times tab 
5. for the Medium format click the hour dropdown and switch it from 1-12 to 00-23 and delete the AM/PM element