Problem with Item Relisting Duration Period on an iPhone

[jcmb2012]

When I relist an item, I use my iPhone if I don't have laptop access at the time.  I'm having  a problem relisting on my iPhone because eBay sometimes changes my original duration length to 'good til cancelled'.  I don't always want the GTC duration, but I can't locate where to reset it back to 30 day (or shorter) duration while in the relisting process on the iPhone.  And once an item is listed as GTC I can't seem to revise the duration; and if I cancel the listing, eBay penalizes me under their seller rating system.  Any input or suggestions are appreciated.