I would set the timeout on the whole AWS SDK operation (not at the http level). In node.js, using bluebird I can wrap the promise object returned by the SDK and then put a timeout on it. e.g.

const Promise = require('bluebird')
...
Promise
  .resolve(dynamodb.get(req).promise())
  .timeout(getTimeout()) // calcaulated from time rem - reserved time for fallback actions
  .catch(err => doFallback())