Are there any limitations placed on the number of API calls that can be made in a given time period or by a specific user.
In most circumstances, there are no limitations to the number of calls that can be made in a day or by a specific user.
The only limitation is made on the ad-hoc endpoint when using basic authentication. The ad-hoc endpoint is not available in version 2 of the API and is being deprecated. For the ad-hoc endpoint, only 16 calls by the same user can be in process at the same time.