Hi, these fields are held in plan snapshots. See https://jazz.net/library/article/658.
There are numerous articles around planning in the library: https://jazz.net/library/ you might want to run this query and look at them: https://jazz.net/library/#tag=planning

For the immediate answer, if you are using traditional process template use:

   start date -> constraint date with "Start No Earlier Than"  (in English, other language varies).
   end date -> due date

However, these are not planned ones. Planned ones are kept in snapshots (as Ralph mentions). These value may be different from constraint date/due date. If there are more works assigned to one person during specified periods, RTC automatically calculates realistic ones. For example, if there are 5 WI which has duration of 2 days, and start end date of each work items are within 1 week, then this is wrong.

I see that creating iteration of 2 weeks or 1 month for traditional plan (not iterative, but just cut into several phases so to speak) is good way to manage work items. By this way, project manager should be able to handle tasks for traditional project much better in RTC.