Equipment can be off rent and still unavailable for the next job. Preparation, outbound transport, collection, cleaning and inspection occupy time even when the customer is not using the equipment. A rental availability window should represent those operating constraints.
Separate customer dates from stock dates
Keep the customer's use period clear for commercial purposes. Separately identify when stock must be ready for preparation and when it will be released after return. Do not silently change the billed period just to make an availability calculation work. The two date ranges have different purposes and should be explainable.
Turnaround allowances should reflect the work required for the category. A quick count may be enough for one item; another may require testing or reassembly. Use observed operating requirements and your applicable procedures. An arbitrary universal buffer can either block useful capacity or create an impossible plan.
Test consecutive fictional jobs
Acme Demo Co expects ten Category A units back at 12:00. A second job needs those units picked at 13:00 for a 14:00 departure. Unloading and inspection are planned to finish at 15:00. The customer periods may not overlap, but the operational windows do.
The team could change the first collection, use different ready stock, adjust the second departure with approval or source another supply. Removing the inspection allowance from the plan does not make the equipment ready sooner. The quantities and times are invented to illustrate the scheduling issue.
Update estimates when facts change
An expected return is a planning assumption. A received and inspected quantity is evidence. Keep those concepts separate, and update dependent jobs if transport or receiving runs late. The person handling the delay should be able to see which preparation windows depend on it.
At the daily planning check, review consecutive jobs with short turnaround, uncertain collections and equipment awaiting inspection. Record the earliest credible ready time and the person responsible for the next update.
Once a week, compare planned and actual turnaround for a small set of completed jobs. Use the differences to improve allowances, while retaining any required safety checks. A better buffer is based on the work your operation performs, not on making the availability screen look full.