There is no set interval to replace a windscreen washer pump. When you have symptoms like no washer fluid coming from the washer nozzles, or another of the symptoms listed it is possible the washer pump may need replacing. At an inspection the mechanic will establish, step by step, what the exact fault in the electrical system is before replacing any parts.
Please note, though, when there is no washer fluid being distributed over the window it is not necessarily the washer pump that has failed. In some cases it might be that the wiper switch has failed or that the system has blown a fuse. Equally it could be a loose or corroded wire connector.