import { shaderMaterial } from '@react-three/drei'

const CustomMaterial = shaderMaterial({ time: 0 }, vertexShader, fragmentShader)
const material = new CustomMaterial()
material.onBeforeRender = () => material.time++

import { extend, ThreeElement } from '@react-three/fiber'
import { shaderMaterial } from '@react-three/drei'

const CustomMaterial = shaderMaterial({ time: 0 }, vertexShader, fragmentShader)

declare module '@react-three/fiber' {
  interface ThreeElements {
    customMaterial: ThreeElement<typeof CustomMaterial>
  }
}

extend({ CustomMaterial })
// alternatively,
// const Component = extend(CustomMaterial)

<customMaterial time={0} />