Withdrawals have different execution timings, depending on the destination:
Mainnet: 3 hours
Arbitrum, Optimism, Base: minutes (depending on bridge congestion)
In addition, Aevo constantly and randomly selects some withdrawals for additional security checks. If your withdrawal is selected, it will enter in a "flagged" status.
Flagged withdrawals are processed in 60 minutes (you'll see a countdown clock next to your transaction, in your portfolio section) and subsequently executed.