_Time in Shader is unstable, so the uv move is not smooth.

Hi,
I need a simple uv move anim for wall in my proj, I use just simple shader as blow:

v2f vert (appdata v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
o.uv = TRANSFORM_TEX(v.uv, _MainTex);

float offset = _Time.x * _Speed;
o.uv.x = o.uv.x + offset;

return o;
}

It works fine on PC, but on mobile phone, the uv move is not smooth, very unstable. I think it's because the delta time is stable un PC, but not stable on phone, so the _Time change is unstable too. But how could I fix it, in my shader?