QS:Time limit warning
From LimeSurvey Manual
Time limit warning message timer (time_limit_warning)
Description
Sets how long (in seconds) before the time limit expires to display the time_limit_warning_message. Setting a value for this attribute turns on the time limit warning message.
This settings is only applicable if the general Time limit settings is activated. This setting also exists for a second warning message.
Example
If you set this to '20' then the time limit warning message will appear 20 seconds before the time limit countdown reaches zero.