有效期自xx时间开始，常见的表达有3种：

1. commence on

2. shall be from......to

3. shall start from......and end on

例句1

The Partnership’s term shall commence on the date of April 25, 2016(“Initial Date”) that all Limited Partners are registered in the Parallel Fundin PRC and shall continue for three (3) calendar years, unless earlier wound upand dissolved by the General Partner. 

合伙企业的有效期自2016年4月25日（“初始日期”）开始，在该初始日期全部有限合伙人在中华人民共和国Parallel Fund注册，且除非由普通合伙人提前停止或解散，该有效期将持续三（3）个日历年。

例句2

The Term of this Agreement shall be from 1 December 2008 to 1 December 2009,subject to earlier termination in accordance with Article 11 of the Terms & Conditions,upon which this Agreement shall expire automatically.

本协议有效期自2008年12月1日到2009年12月1日,受制于根据第11条条款及条件提前终止之约束,本协议应自动失效。

例句3

A Guarantee Period of 12 months shall start from the date of Equipment Acceptance Certificate or 14 months start from the date of B/L, whichever comes earlier.

质保期应为设备验收证书签署之日起12个月，或海运提单日后14个月，以先到者为准。