The freight window decides when a tour can happen, so book it before you book the tenant
In most markets scheduling a walkthrough is a calendar problem, and here it is a building problem.
Access in this city is controlled: lobby desks, sign-in, service entrances, elevators with scheduled hours. A confirmed time with a tenant that has not been confirmed with the building is a time you will move, and a moved walkthrough is where interest dies.
Work the constraint into the process rather than around it. Keep a current note per building on who to call, what the access hours generally are and how much notice is typically needed, and check it before you offer a slot.
Offer two windows, not an open calendar. An occupier choosing between two times you already know are workable converts better than one asked to propose a time you then have to retract.
Confirm in writing what the tenant needs on arrival: which entrance, which desk, whether identification is required. A tenant standing on the wrong side of a building at nine in the morning is a tenant you have already annoyed.