I really don't think this question was meant to be 'solved' in the traditional manner by breaking it up into minutes etc., though all the approaches above that have done that have been analytically correct. Each one of these approaches is valid, and would in fact have been needed if there had been more than one option ending with a 0. However, that is not the case here and we must try and look for a quicker method. The GMAT does not usually require test-takers to enter into laborious calculations, so we must look for some other way to solve this.
As pointed out by Bunuel and PareshGmat, one must look at the last digit. If it is 6:27 now, what time would it have been 7 minutes earlier? 6:20 (notice the 0 at the end). How about 27 minutes earlier? Again, a 0 at the end. 277? 222777? Again, no matter what, will end with a 0. Therefore, looking at the options, we can quickly conclude that this would end with a 0 and then choose D.
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