Q:

cron every X exact meaning

In cron you can specify */n where n means every n times period, for instance in the first column is minute.
*/5 means every 5 minutes, but which minutes? 0, 5, 10, ...?

What happens if the number specified is not a divisor of 60?
*/7 what will happen, will it start to skew in the next hour?

A:

It'll go on 7, 14, ... 56, 0, 7, 14, ...
With that syntax, I like to think of it as going when t mod x === 0

A:

In crontab, * is a shorthand for first-last (where first is the minimum possible value and last is the maximum possible value).
The syntax first-last/step means "every N where N >= first and N <= last and (N - first) % step == 0".
So */7 in minutes means the same as 0,7,14,21,28,35,42,49,56.  But 1-59/7 means 1,8,15,22,29,36,43,50,57.

