A booking that ends today blocks a hire starting today

It should not. Ranges are treated as half-open: a booking that ends on the 10th releases the 10th for a hire that starts on the 10th, so back-to-back hires do not lose a day of turnover. If a same-day turnaround really is being refused, the cause is a different overlapping booking or a blocked date on that day, not the end date of the earlier one.