1.调整节点相对位置

其中hourTrans,minuteTrans,secTrans为空节点
hour,minute,sec为一个quad.
调整好相对位置，可以使得指针绕端点旋转的效果

2.脚本挂载在clock节点上，为空节点

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Clock : MonoBehaviour
{
    private const float hours2Degree = 360f / 12f;

    private const float minute2Degree = 360f / 60f;

    private const float sec2Degree = 360f / 60f;

    public Transform hour;

    public Transform minute;

    public Transform sec;

    public bool useTimeSpan = false;
    // Start is called before the first frame update
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        if (useTimeSpan)
        {
            TimeSpan ts = DateTime.Now.TimeOfDay;
            hour.localRotation = Quaternion.Euler(0f,0f,(float)ts.TotalHours * -hours2Degree);
            minute.localRotation = Quaternion.Euler(0f,0f,(float)ts.TotalMinutes * -minute2Degree);
            sec.localRotation = Quaternion.Euler(0f,0f,(float)ts.TotalSeconds * -sec2Degree);
        }
        else
        {
            DateTime time = DateTime.Now;
            hour.localRotation = Quaternion.Euler(0f,0f,time.Hour * -hours2Degree);
            minute.localRotation = Quaternion.Euler(0f,0f,time.Minute * -minute2Degree);
            sec.localRotation = Quaternion.Euler(0f,0f,time.Second * -sec2Degree);
        }
    }
}

3.裁剪像素的shader,PS用不熟，效果不好。
shader代码

Shader "Custom/AlphaTex"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _MaskTex ("Texture",2D) = "white"{}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            sampler2D _MaskTex;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = tex2D(_MainTex, i.uv);
                fixed4 mask = tex2D(_MaskTex,i.uv);
                if(mask.r < 1e-4){
                    discard;
                }
                return col;
            }
            ENDCG
        }
    }
}

贴图和遮罩

效果如下: