(1) An alien admissible in E-1, E-2, E-3, H-1B, L-1, or TN classification and his or her dependents may be admitted to the United States or otherwise provided such status for the validity period of the petition, or for a validity period otherwise authorized for the E-1, E-2, E-3, and TN classifications, plus an additional period of up to 10 days before the validity period begins and 10 days after the validity period ends. Unless authorized under 8 CFR 274a.12, the alien may not work except during the validity period.
(2) An alien admitted or otherwise provided status in E-1, E-2, E-3, H-1B, H-1B1, L-1, O-1 or TN classification and his or her dependents shall not be considered to have failed to maintain nonimmigrant status solely on the basis of a cessation of the employment on which the alien’s classification was based, for up to 60 consecutive days or until the end of the authorized validity period, whichever is shorter, once during each authorized validity period. DHS may eliminate or shorten this 60-day period as a matter of discretion. Unless otherwise authorized under 8 CFR 274a.12, the alien may not work during such a period.
(3) An alien in any authorized period described in paragraph (l) of this section may apply for and be granted an extension of stay under paragraph (c)(4) of this section or change of status under 8 CFR 248.1, if otherwise eligible.
这 10 x 2 天的宽限期，是为了给申请人「准备开始工作」、以及「准备离开美国或延期/转换身份」（[…] two grace periods of up to 10 days for individuals in the E-1, E-2, E-3, L-1, and TN nonimmigrant classifications to provide a reasonable amount of time for these individuals to prepare to begin employment in the country and to depart the United States or take other actions to extend, change, or otherwise maintain lawful status），需要 CBP/USCIS 给你才行，并非自动享有。