You can use instead:
javax.jcr.Session jcrSession = LifeTimeJCRSessionUtil.getSession("website");
Node mynode = jcrSession.getNode("/my/node/path");
info.magnolia.cms.core.MetaData metaData = info.magnolia.jcr.util.MetaDataUtil.getMetaData(mynode);
String template = metaData.getTemplate();
Basically, instead of getHierarchyManager("website").getContent("mynodepath")
you should use
getSession("website").getNode("/my/node/path")
.