I would like to express that an action should be done every three weeks, but that longer periods are also acceptable.
Which of the following is the simplest, clearest, and most natural way to express that? And if any of the expressions below are problematic, in what way are they?
Take the pill:
- Every three weeks or more
- At least every three weeks
- Every three or more weeks
- Every three weeks or longer
- Every three weeks or less frequently