Provided are a method by which a first device performs wireless communication and a device supporting same. The method may comprise the steps of: obtaining information related to a resource pool; obtaining one or more sidelink (SL) discontinuous reception (DRX) configurations; selecting a destination having a highest priority logical channel from among logical channels having available SL data; generating a medium access control (MAC) protocol data unit (PDU) on the basis of at least one logical channel belonging to the destination; determining a packet delay budget (PDB) on the basis of a PC5 5G Quality of Service (QoS) Identifier (5QI) (PQI); on the basis of sensing, determining a plurality of candidate resources in the resource pool within a selection window; and selecting a transmission resource for SL transmission to a second device associated with the destination from among the plurality of candidate resources.