animation shader problem

I code the shader with CG. I want to animate textures from one to another using time.

                 float3 Mask = tex2D(_MaskMap,i.uv);
                 float3 CurrentColor = tex2D(_EntryTexture,i.uv);
                 float3 DestiantionColor = tex2D(_DestinationTexture, i.uv);
                 
                 float animateColor = _Time.x/256;
                 
                 if(Mask.r == animateColor && Mask.g == animateColor && Mask.b == animateColor)
                 {
                     CurrentColor = DestiantionColor;
                 }
                 
 
                 return float4(CurrentColor,1);

this is my pixel shader.

Mask is texture that made of color RGB(0,0,0) ~ RGB(255,255,255)

The mechanism is that first, read mask and change texture color from currentColor to DestinationColor.

this runs RGB(0,0,0) ~ RGB(255,255,255)

The things I dont know is _Time's value(sec Unit? ms Unit?). and if statement( if(Mask.r == 192/256) : this is not work. ).

I need your help T.T