The problem comes when you specify a pattern rather than an interval.
Technically, it's the period you want to set, not the frequency. Frequency being the number of occurrences of a repeating event per unit time vs period as the duration of time of one cycle.
When you specify a pattern like every X at Y you have to say things like:
- every day at time T
- every week but on day D, at time T
- every month but on day n at time T
The event occurs when the pattern is matched.
When you specify an interval you say things like
- every N days starting at time T
- every N weeks starting at time T
- every N months starting at time T
The event occurs when the interval elapses.
So with intervals you only ever have to specify the same pair of values:
- the interval (N + unit)
- when to start (for which NOW might be an option)
bvckup is an awesome backup tool that uses exactly this structure: