What is the "Default Timeout" value in SQLite connection string used for?
I found this out by looking at the source code: The timeout value of a command is initialized to DefaultTimeout and passed to the internal SQLite3.Prepare function.

This is used to control a loop that automatically retries statements that fail with a Locked or Busy error.  When the timeout has expired (as measured by Environment.TickCount), then an exception is thrown with whatever the most recent error code was.  Otherwise, it sleeps for a random amount of time (between 1 and 150 ms) and tries again.