XPLM_API void       XPLMSetFlightLoopCallbackInterval(
                         XPLMFlightLoop_f     inFlightLoop,    
                         float                inInterval,    
                         int                  inRelativeToNow,    
                         void *               inRefcon);    

This routine sets when a callback will be called. Do NOT call it from your callback; use the return value of the callback to change your callback interval from inside your callback.

inInterval is formatted the same way as in XPLMRegisterFlightLoopCallback; positive for seconds, negative for cycles, and 0 for deactivating the callback. If inRelativeToNow is 1, times are from the time of this call; otherwise they are from the time the callback was last called (or the time it was registered if it has never been called.