687 comes by summing up current reading (123) with Cycle frequency (564).
From Current reading 123 to reach 687, it will take 7 days (564 / 80), System considers the date of 16/06/2014 to calculate 23/06/2014.
Whenever you change the Maintenance Plan scheduling parameters or Cycle frequency, Maintenance plan should be restarted to generate the new schedule lines.
And, by changing some data in existing plan & based on system response, we can't predict the system calculation. We can give you the suggestions on how all the parameters should be maintained in Maintenance plan & Measuring Point (in case of Performance based plan) to generate the order in specific way.
As we can't make replica exactly what you made, it will be never possible to give proper advice on system behavior.
If you want to see the calculation behind date calculation, select the particular row in IP10 & click "Calculator" button. There you can see the calculation.
Measurement document should be created while doing TECO of PM order. In TECO pop up, you can find the button as "Create Measurement document".
Refer this blog which has been created by considering your scenario.
