Under More → Contacts you maintain other people's schedules – for example colleagues or family members. Up to 5 contacts are free.
With the + you choose Add manually or Add via Nearby. For a manual contact you set a name and color, save it and then maintain their schedule: with Add day you enter a date, either All day or with a from and to time. It is only about when the person works – no wages or overtime.
The free limit is 5 contacts; more will require a subscription later. Removing a contact also deletes their schedule and sharing settings.
In Plan, use the Who selector to switch from Me to a contact. You can only view their schedule there, you cannot edit their entries.
If the other person uses the app too, you take over their schedule directly from device to device – no account, no cloud:
In the Sharing settings of a Nearby contact you choose per employer whether and how much of your schedule they can see: Presence only (just the days) or With times. Without your own choice, an employer is shared.