Hey zapier folk,
I had the problem that for a customer a Zap has to be executed every two weeks. I would like to present my solution to you and I'am open to alternative solutions or issues I haven't considered.
First I used the trigger "Schedule by Zapier" and selected "Every Week" as the event.
In a code block I determine the weeks between the current day and the beginning of time (1970 
). After that I determine with the modulo operation whether the week is even (0) or odd (1).
import datetime
date_delta = datetime.date.today() - datetime.date.fromtimestamp(0)
return {"continue" : int(date_delta.days/7)%2}
Then I check with a filter if the Zap should be continued in even (0) or odd (1) weeks.
I hope the description is sufficient.