2 things:
Any response from the clientside code is falsified to make it feel quicker and more responsive than it actually is; the server only receives information based on the game's tick system (every 0.6 seconds). If there's a delay as small as you are mentioning, it is based on the person's computer - not the server communicating. This is how we make all interfaces feel smoother than they are.
Secondly, as some people below have suggested might be the case, the check is only actually done once all numbers have been submitted. Not after each number entered. That'd be silly!
Hope this helps get rid of any fears :P
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