Methods, systems, and devices for wireless communication are described. A non-sidelink synchronization signal (SLSS)-transmitting user equipment (UE) may initiate a channel occupancy time (COT) including multiple contiguous slots and a gap slot. The non-SLSS UE may detect an SLSS UE (capable of transmitting sidelink synchronization signal blocks (S-SSBs)) and assume that the gap slot will be filled with an S-SSB. The non-SLSS may transmit a sidelink message during the COT after the gap slot, based on the assumption. Alternatively, based on the SLSS UE indicating that it is capable of transmitting the S-SSB, the non-SLSS UE may schedule transmission of the S-SSB such that the gap slot is filled. If the SLSS UE is incapable of transmitting the S-SSB, the non-SLSS UE may determine a method for transmitting the sidelink message during the already-initiated COT or during another COT.