Export data grouped by visitId

Hello everyone,

couldn´t find anything on this topic so here is my problem.
I try to export data from piwik for cluster analysis. I want the data to be grouped by the visit ID.
I run this command for the export:

http://www.mysite.com/piwik/index.php?token_auth=g456435rewfwet435364&format=xml&idSite=5&period=year&date=2013-06-10&language=en&module=API&method=Live.getLastVisitsDetails&showColumns=idVisit,visitIp,visitorId,visitorType,visitConverted,actions,visitLastActionTime,visitDuration,visitCount,location,referrerName,referrerKeyword,operationgSystem,browserName,serverTimePretty&group=idVisit

My problem is the date of the visit. With serverTimePretty i only get times like 23:55 ±4 minutes. This can´t be true and i don´t want the time, i want the day an month.
Can anyone help me with that?

Thanks!