The FTE (or the working time) is an element resulting from the national legislation.
On the one hand, the obligation included in the GA is twofold:
a) exclusive dedication (i.e., only activities indicated in the technical annex) and
b) full-time dedication regardless of the working time (i.e., no part-time).
If both conditions are fulfilled the secondment is in principle eligible.
On the other hand, the obligation is referring to the “research activities” of the project: this means that, as long as the staff member is dedicated full-time to these activities (those latu sensu included in the description of the project), then it is allowed.
It is the responsibility of the beneficiary to ensure that the research activities performed are consistent with the description of the Staff Exchanges project, even if (partially) funded elsewhere, provided that this will not result in double funding.