Broadly speaking, it is normal practise to double the call volume figure before applying it to an Erlang calculation which normally expect hourly figures.
If you are using Westbay Traffic Calculators or Erlang for Excel, then that is what you will need to do. If you are using Ansapoint, then you have the opportunity to create projects with either 60 minute or 30 minute durations. If you select 30 minutes, then you can enter your figures directly.
If you have one product, but would like to buy the other, then you will be entitled to a 10% discount on your subsequent purchase. To qualify, you must purchase through your account page at http://www.erlang.com/download/.