New recurring task type: x days after finishing the previous instance

As a user who is managing his private tasks with To-Do, I have a number of recurring tasks in which the date of the next instance depends on when I finished the previous one, even if I finished that one later than originally intended. Examples:

• I have a recurring task to get a haircut every 4 weeks. But sometimes, I go to the barber shop a few days or even a week later. So, next time the due date is to be set for the day when I got the haircut + 4 weeks. I constantly need to adjust the series or create single tasks instead, which both is a PITA.
• In my second home, I buy WiFi vouchers every 30 days. But sometimes, I am travelling and returning to the apartment a few days or weeks later, so I buy the new WiFi voucher when I need it. But then, the next one is due 30 days after I started using the current one.
• When abroad in a certain country, I need to report my whereabouts to immigration every 90 days latest. But depending on when they process my application, the due date for the next report might deviate and be a few days earlier, i.e. issuing date + 90 days.

In all these cases, I want To-Do to ask me when ticking off the current instance, on what exact date I finished the task, the suggested default being the current date (today's date). Then, after I confirmed or changed the date, the next instance of my recurring event should be that date + x days/weeks/months, depending on how the series is defined. BTW, I also need the same feature for Outlook events when working in an enterprise context.