An optimistic rollup assumes transactions are valid unless challenged during a fraud-proof window.
Withdrawals to L1 can take days because of challenge periods, unless third-party liquidity bridges are used.
In research workflows, Optimistic rollup is usually interpreted with Layer 2, Arbitrum, Optimism, and Fraud proof rather than as a standalone signal. Throughput, finality, and fee markets determine user experience and where activity migrates during congestion.