Charge activity planified in future

Of course.
There is no constraint on this side.

The reallity is so often different from plannification !

You can also, if you need, enter some real work in the future : for instance for administrative projects (holidays), or if you want to reserve a day for a specific booked activity (training, meeting, ...). This way, you will avoid planning other activiites on this day.

Just go to the "real work allocation" screen : you will see the activity, and just enter your real work.