Or you could do a 'soft boot'.
Press the Help button on the ntl remote.
Press the Yellow button and the whole thing reloads.
I tend to do this each day, if only to get the EPG to refresh.
The clock being an hour out happens to me every now and then. At least it is consistently an hour out (i.e. the EPG start times are also wrong) so auto tune for programme recording is not affected.