Long response times may be annoying, but unpredictable response times are worse. It can be very stressing to the user if answers sometimes come fast and sometimes take a long time. This problem is often seen in network systems. You may use local rather than central storage and computing power whenever possible in order to reduce this problem.
There should be an immediate feedback to every command the user gives the system. If the final result is delayed then there should be a temporary feedback to tell the user that the command has been received and that the system is working on it. At least the system should indicate that it is working by showing an hourglass, a watch, a turning wheel, or something similar. But preferably, there should be a progress bar or countdown giving the user a chance to estimate how long time the operation will take.
There should always be a way to cancel or abort time-consuming operations before they are finished.
If the system is capable of setting commands with long response times in a queue and serve them on a first-in-first-out basis, then there should be a way to watch the queue and perhaps also to delete commands from the queue or change their priorities. If no watching of the queue is possible, then the system should rather have no queue at all (at least not for operations that take more than a few seconds). A system with no queue should either refuse to accept any new commands before the execution of the previous command has been finished or canceled, or it may be constructed so that a new command always cancels any previous unfinished operation.