It RETARDS the cam timing, does not advance it. Unless a serious amount of material was removed, don't worry about it. You'll have bigger problems if that's the case anyways like piston to valves hitting.
It can be advantageous to retard the intake cam 6-8* according to solo miata. The exhaust side shouldn't do too much. Each tooth is 12* for reference.
If this was a head shaved just to straighten it out, I doubt anymore than .010" was removed. Unless this is a performance shop building for compression I wouldn't worry, even .010" is past manufacturer spec (.008 for 1.6 .004 for 1.8). I know you can shave .030" without any worries on a 1.6, although I have read as high as .045". Their engines might be interference now though.