That's because double division often lead to a loss of precision. Said loss can vary depending on the order of the divisions.
When you divide by 7d, you already lost some precision with the actual result. Then only you divide an erroneous result by 60.
When you divide by 7d * 60, you only have to use division once, thus losing precision only once.
Note that double multiplication can sometimes fail too, but that's much less common.
