Yes it is.
The order in which you stop/start the services is unimportant.
Make sure your customer picks a moment when there are no AccessPoint visitors and no scheduled Publisher reloads.
For more information, see here: QlikTip #29: Restarting/Stopping/Starting services in QlikView 10
That should work fine. Just create 2 .bat files, one to stop the services:
NET STOP QlikviewDirectoryServiceConnector
NET STOP QlikViewDistributionService
NET STOP QlikviewManagementService
NET STOP QlikviewServer
NET STOP QlikviewWebserver
Then another to restart them:
REM Starting Qlik Services
NET START QlikviewDirectoryServiceConnector
NET START QlikViewDistributionService
NET START QlikviewManagementService
NET START QlikviewServer
NET START QlikviewWebserver
And then schedule the running of the 2 bat files.
Another option if you didn't want to actually restart the services, but rather to clear the cache of the QVS and reduce the memory amount used at the time, would be to set the ClearCacheTimesPerDay=1 in the settings.ini file, you'd add this under the [Settings 7] section, located in C:\ProgramData\QlikTech\QlikViewServer (on my server)
This would clear any cache built up by the QVS service once a day, setting this to 2 would be twice a day and 3 for three times, the clear would be done at equal intervals during the day.
However the cache is built for a reason and the server should be configured and sized to allow your document and server loading, clearing the cache would slow things down a little as the QVS would then have to re-calculate values and slowly build the cache back up, but it would of cause depend on your customers specific setup etc.