Consider:

Human: "You see, our planet's date/time system is very simple. First, the revolution of our planet around the sun is divided into 365 units, called days. Those days a--"
Not Human: "365? Is this number significant?"
H: "Uh, well.. no, not really. As I was saying, days are further divided into 24 units, called hours."
NH: "And the number 24 is chosen at random, too?"
H: "... yes."
NH: "Continue."
H: "Hours are divided into 60 segments, or minutes. Which are divided into 60 segments called seconds."
NH: "*CZZZRK* Number Six, schedule this planet for termination *CZZZRK*"
H: "Wait! We have a system for keeping track of our days, called a calendar. There's a nice pattern to this one: Seven days in a week, fifty two weeks in a year. But there's also twelve months in a year, and four weeks in a month. Sort of. Really it's a little more. There's 30 days in a month, but sometimes 31, and one month has 28. Except every four years it has 29, an--"
NH: *Head explodes*

As you can see, we have a significant advantage over any hostile force. Especially if they're programmers. Because they'll go nuts and kill themselves if they have to manipulate date/time in a program.