by confirmed L/C payable by draft at sight to be opened 30 days before the time of shipment.

问题描述:

by confirmed L/C payable by draft at sight to be opened 30 days before the time of shipment.
其中的to be opened 30 days 怎么翻译?

装船前30天开立凭即期汇票付款的保兑信用证.
to be opened 30 days before the time of shipment——装船前30天开立(信用证).