Lightning - adjust the time between lightning

[Sunny-Sol]

Hi, is it possible in the code to adjust the time frame between every lightning strike?
Somehwere here in the file rain.frag i guess

    if(u_lightning) {
        float lightning = sin(t * sin(t * 10.));				// lighting flicker
        lightning *= pow(max(0., sin(t + sin(t))), 10.);		// lightning flash
        col *= 1. + lightning * fade * mix(1., .1, 0.);	// composite lightning
    }
    col *= 1. - dot(UV -= .5, UV) * 1.; // vignette

    gl_FragColor = vec4(col * u_brightness, 1);