Not exactly sure what you are trying to accomplish this with with (the code type) but GTC is "Good 'Til Cancelled -for FixedPriced an I think Classified. Three Days is expressed as Days_3 and is good for most type listings. Maybe list the code for a better answer.
That I would like to do !! if I put GTC FixedPriceItem I get two errors : Handling time is required. Handling time is required. 21916389 Duration Invalid. The duration "GTC" day(s) is not available for this listing type, or invalid for category "2562". 83