Work backwards from the day the person genuinely needs to be on site, allowing for preparation, any filing, a visa step where it applies, admission, and the lawful start of work. If the calendar does not fit, change the assignment dates rather than compressing steps nobody involved controls.
Protect the far end as well as the start
Assignments slip at the end more often than at the beginning. Fix the date by which an extension question must be raised, allowing time for legal review of the individual history and any limits that apply, and identify who owns that decision on both sides. Also plan the return: notice on housing, school placements, and the overseas role's availability all need lead time.
Add one date at the far end that is easy to leave unowned: the point at which the person's return has to be arranged on the other side. An overseas role held open, a team expecting them back, a replacement whose own contract ends — each has a lead time, and each belongs on the same calendar as the extension question rather than on a separate one kept by a different department. Hypothetical example: an audio mastering workflow specialist's assignment carries a stated end date, and the calendar records not only when an extension question must be raised but when the overseas employer must decide about the temporary cover, because those two decisions constrain each other and are usually taken by people who are not in the same conversation.