So you want to authenticate as "User A" and create the item, but want to display in Podio that the item was created by another name at an earlier time?
That's not possible. You will have to create Podio users with the same name and authenticate as the user with the correct name to achieve that effect. Perhaps you should rather use app authentication, then it will say "created by [app name]".
The timestamp will always show when the item was created in Podio, it's not possible to change the timestamp via the API.