Can a freight company change delivery terms after I have already booked?

Whether the company can vary the terms depends on what you actually agreed to and the specific wording of any variation clause. If the booking confirmation or contract stated that delivery times are estimates only, and included a clause permitting reasonable variation, the company may be within its rights, provided the change is reasonable and not applied in bad faith. If, however, the agreed delivery time was a firm, guaranteed term of the contract, a unilateral change without your consent could be a breach, entitling you to damages for losses that flow from the delay, subject to the terms limiting liability. Check whether the change is materially significant to your purposes, such as a critical deadline you notified them of at booking, since this can strengthen a claim. Communicate in writing, request confirmation of the reasons for delay, and assess your options under the specific contract terms.