During the period of visa validity, the L-1 visa holder can request to recapture full days spent outside of the United States to add back to the maximum time. The burden of proof falls on the petitioner to provide relevant evidence such as I-94s, passport stamps, plane tickets, etc. The reasons for travel outside of the United States, whether it be for business or personal reasons is not pertinent to recapturing time, so long as the visa holder can successfully demonstrate that he/she was outside of the United States for the time he/she is requesting to recapture. In some circumstances, an L-1 visa holder may not be granted all of the requested time if there is not sufficient evidence to withhold the claim.
For more information on L visa, please refer to the following links: