合同签定后90天之内中国发货。用英语是

90天内--within 90 days

翻译：

The goods will be shiped within 90 days from China after the contract is signed by both sides

注意，不压少了both sides,单方面签的合同不会有效。

(It will) ship from China in 90 days after the contract is signed.

shipment will be delivered in 90 days after signing the contract