The current values for search result_type parameter are:
mixed
recent
popular
For that, I think the only way to know the first tweet on new hashtag is to retrieve all its tweets and sorting them by date!
Also, it is expected to have difficultly with the API rate limit.
However, I think it will be great if a new value “first” will be added to the result_type parameter of the GET API.
Moreover, it will be so interesting for Twitter normal users if some tag attached with any hashtag in order to enable the user to know directly who initiate this hashtag.
I appreciate any comments regarding my suggestions…