You figured it out, but because you asked for 'config.dateTimeInfo', it was stored as that hash key.
You could use the get_property() method in the SDK, which will sort of try both forms:
$host->get_property('config.dateTimeInfo')->ntpConfig->server;
Should also work:
$host->get_property('config.dateTimeInfo.ntpConfig.server');
I don't use it much personally, I sort of fall back on the usual Perl hash syntax.