Function XPLMSetFlightLoopCallbackInterval 

pub unsafe extern "C" fn XPLMSetFlightLoopCallbackInterval(
    inFlightLoop: XPLMFlightLoop_f,
    inInterval: f32,
    inRelativeToNow: c_int,
    inRefcon: *mut c_void,
)

XPLMSetFlightLoopCallbackInterval

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.