The following environment variables may be set to alter some MRPT functionality:

MRPT_EXPR_VERBOSE: Set to 1 to enable extra verbose debug traces for mrpt::math::CRuntimeCompiledExpression::eval().
MRPT_CCAMERA_KINECT_TIMEOUT_MS: Timeout in milliseconds to wait for a new frame from a Kinect sensor when using the method mrpt::hwdrivers::CCamera::getNextFrame(). Default: "3000".
MRPT_HWDRIVERS_DEFAULT_LEAP_SECONDS: In mrpt::hwdrivers::CGPSInterface, the default offset from GPS time to UTC time, for use before any GNSS especific message informs on this offset. Default: 17 (valid for 01/2016)
MRPT_HWDRIVERS_VERBOSE: Set to "1" to enable verbose output to cout from all mrpt::hwdrivers classes. Default: "0".
MRPT_WXSUBSYS_TIMEOUT_MS: The timeout in milliseconds to wait in mrpt::gui windows constructors until the wxWidgets thread processes and really creates the window, before reporting an error. It's also used in the function mrpt::hwdrivers::prepareVideoSourceFromUserSelection(). Default: "5000" in Release builds, "30000" in Debug.