Try

op-chain-ops/genesis/genesis.go

@@ -45,7 +45,11 @@ func NewL2Genesis(config *DeployConfig, block *types.Block) (*core.Genesis, erro
 	// L2GenesisBlockNumber is always going to be zero, since there don't seem to be any assignments to
 	// L2GenesisBlockNumber in the codebase so it must only be set by deserializing config, and running the tests and
 	// inspecting the value of L2GenesisBlockNumber revealed only zeros.
+
 	var cel2Time uint64
+	if config.L2GenesisBlockNumber > 0 {
+		cel2Time = *config.RegolithTime(block.Time())
+	}
 	optimismChainConfig := params.ChainConfig{
 		ChainID:                       new(big.Int).SetUint64(config.L2ChainID),
 		HomesteadBlock:                big.NewInt(0),