It's perfectly fine to wait if you're concerned about high fees, as the ETH will be securely held in the bridge.

If you don't claim your ETH via the Sui bridge, it will stay on the bridge in a 'claim' state until you decide to claim it. There's no immediate rush; however, the funds will not automatically revert back to the original platform (Sui in this case) or disappear, and will be waiting for you to claim when you're ready.