Yes, it's an annual service.
There are number or O-rings, tubes and filters to replace. That bit is pretty quick.
Running through the checks, tests and calibrations can take several hours. Assuming the machine was running error free prior to the service we usually advise the home patient we'll need 'upwards of half a day'. On a straight forward machine with a 9am-ish start, and a following wind we're packing up to leave by late lunch time. If we find temp cals are required you can add at least another hour. If the dummy at the treatment at the end isn't satisfactory, or you discover other faults along the way you'll wish you'd brought your sandwiches.
We usually service exchange the WRO at the same time (which gets serviced back at base).