HubSpot only supports “date-time” display and function only for to DEFAULT system properties, but not CUSTOM properties. Documentation is a bit misleading and says it can intakedatetime values via import or API, but it leaves out that it will strip them of the “time” when importing to custom properties.
It will only keep the “time” if you are importing to a defaultdatetime field (activity date, meeting date ,create date, etc)
Please allow the creation AND import of true date-time values in custom properties. Even a new custom property type to support this would be welcome.