Colloquially the first could be okay but certainly the latter is the right one to use in most circumstances. The more common ones - five to, ten to, quarter to, twenty to and twenty-five to - are all used without 'minutes' as they are such regular ones everyone immediately knows what they mean. The less-used numbers - such as seven - need 'minutes' added to them because they aren't obviously about the time as they are infrequently heard.
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Ask QuestionsIt's seven to nine.If the number of minutes is not a multiple of five, it's better to say the hour and number of minutes after the hour.