I know that this is a very basic question. But how can I introduce fortnightly data in Gretl?. I have a series hotel occupancy delivered each two weeks and I want to analyze it.

I have used gretl GUI with the non-standard frequencies, but my result is always non-sense. If I use 24 frequencies (12 months x 2 pairs of weeks) Gretl interpret them as 'hourly' data.