See API output: http://demo.piwik.org/?module=API&method=API.getProcessedReport&idSite=7&apiModule=VisitTime&apiAction=getVisitInformationPerServerTime&format=xml&token_auth=anonymous&date=yesterday&period=day&filter_truncate=5
(In [4651]) fixes #2335 queueing the renaming filter fixes the problem
Looks like it occurs again, see for example the following url or the original url from the ticket:
http://demo.piwik.org/index.php?hideMetricsDoc=1&showTimer=0&filter_limit=40&period=day&date=today&idSite=7&flat=0&filter_truncate=4&apiModule=VisitTime&apiAction=getVisitInformationPerLocalTime&sortOrderColumn=nb_visits&filter_sort_column=nb_visits&module=API&token_auth=anonymous&format=json&method=API.getProcessedReport&language=en&
It seems to work in Piwik 2.0. Closing for now.