In many European countries, a month-long notification is a typical period. Assuming there is trust, the transition may take some time. Reworking presentations,

In many European countries, a month-long notification is a typical period. Assuming there is trust, the transition may take some time. Reworking presentations, leaving projects in the middle creates extra work. Plus for the individual, this gives time to adapt to the new situation. However, if you go that route make it specific it is for transition and once person is done it doesn't have to do any new work and just left them to leave earlier.