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The regulations provide for the admission of H-1B workers for the period of validity of the H-1B petition plus a 10 day grace period. This means that the H-1B worker should be admitted for the duration of the H-1B PETITION and not just only the duration of the VISA STAMP (shich might be shorter than the petition) PLUS an addtional 10 days.

See 8 CFR 214.2(h)
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(13) Admission.

(i) General.

(A) A beneficiary shall be admitted to the United States for the validity period of the petition, plus a period of up to 10 days before the validity period begins and 10 days after the validity period ends. The beneficiary may not work except during the validity period of the petition.

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