How do I change the Time Warning? (BlitzIn)

Menu above: Edit > Settings > A window opens with Tabs above it. Click on 'Board/Pieces'
In the down right corner you will find the options for 'Time'.
To turn the warning on check 'Low On Time Warning'.  Unchecking will turn it off.
You can also set the amount of seconds you want to get a time warning.  Example: 30 will give a warning when 30 seconds left.
   
When done click on OK.