Snapdragon (dragon flight) Optical flow question

Dear engineer, help me please.

I did in the below site to bring up optical flow. And I check about whether PX4 recieve optical flow data by ORB.
-> I check opticflow data recieving is ok at orb_copy(ORB_ID(optical_flow), _optical_flow_sub, &optical_flow) / task_main function / EKF2.cpp / PX4.
but ekf app reject opticflow data. because delta_time_good is not good. delta_time_good condition is that dt of optic flow is upper 50 msec .
-> _ekf.setOpticalFlowData(optical_flow.timestamp, &flow);, this function reject optcal flow data.

Reject reason is delta_time ( flow->dt ) is 0.03 ,the function demand
the function is judged to delta_time_good is OK if delta_time ( flow->dt ) is in 50msec undercondition.

So I check delta_time ( flow->dt ), but delta_time ( flow->dt ) is always 0.03 ~ 0.035.

I think that delta_time ( flow->dt ) is time gap between optical flow data get time gyro sensor data get time.
I think I can not control this time gap.
I want to see stable hovering by optical flow.
please help me. thank you.

void EstimatorInterface::setOpticalFlowData(uint64_t time_usec, flow_message *flow)
if (!_initialised) {

// limit data rate to prevent data being lost
if (time_usec - _time_last_optflow > _min_obs_interval_us) {
    // check if enough integration time
    float delta_time = 1e-6f * (float)flow->dt;
    bool delta_time_good = (delta_time >= 0.05f); // this is problem point 

    // check magnitude is within sensor limits
    float flow_rate_magnitude;
    bool flow_magnitude_good = false;

    if (delta_time_good) {
        flow_rate_magnitude = flow->flowdata.norm() / delta_time;
        flow_magnitude_good = (flow_rate_magnitude <= _params.flow_rate_max);

    // check quality metric
    bool flow_quality_good = (flow->quality >= _params.flow_qual_min);
    //ECL_INFO("%d  delta_time %f ",delta_time_good, (double)delta_time );

    if (delta_time_good && flow_magnitude_good && flow_quality_good) {
        flowSample optflow_sample_new;
        // calculate the system time-stamp for the mid point of the integration period
        optflow_sample_new.time_us = time_usec - _params.flow_delay_ms * 1000 - flow->dt / 2;
        // copy the quality metric returned by the PX4Flow sensor
        optflow_sample_new.quality = flow->quality;
        // NOTE: the EKF uses the reverse sign convention to the flow sensor. EKF assumes positive LOS rate is produced by a RH rotation of the image about the sensor axis.
        // copy the optical and gyro measured delta angles
        optflow_sample_new.flowRadXY = - flow->flowdata;
        optflow_sample_new.gyroXYZ = - flow->gyrodata;
        // compensate for body motion to give a LOS rate
        optflow_sample_new.flowRadXYcomp(0) = optflow_sample_new.flowRadXY(0) - optflow_sample_new.gyroXYZ(0);
        optflow_sample_new.flowRadXYcomp(1) = optflow_sample_new.flowRadXY(1) - optflow_sample_new.gyroXYZ(1);
        // convert integration interval to seconds
        optflow_sample_new.dt = 1e-6f * (float)flow->dt;
        _time_last_optflow = time_usec;
        // push to buffer

        ECL_INFO("setOpticalFlowData %f , %f", (double)flow->flowdata(0),(double)flow->flowdata(1));

        //PX4_LOG("setRangeData %f ", *data);


// push to buffer