You are using it correctly, and presumably it is correct in your grammar book sentence; however, the latter is a poor example, because what is also needed is a previous statement, for instance: 'In May of 1985, my wife and I were able to take our second honeymoon. ' A comma after 'home' is helpful in order to distinguish that sentence from a dependent clause: 'At the time my aunt was looking after our children, my uncle was tapdancing in a vaudeville revue'.
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