there isn't a problem provided it has not gone too far.
too far is when it has completely dried out or gone dusty/crumbly.
once the cement has been introduced to water then it is 'on the clock'. it can be reconstituted a number of times but will try and cure more rapidly after each revival. there will come a point when the cement will die.
cement needs water to function, allowing it to dry our rapidly - in the sun for instance, will kill the effect of the cement.
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