Apple reviews each build that they receive. This is a measure of quality control that needs to be considered carefully when submitting new apps and updates to existing apps.
Apple will not specify a specific duration, but the general timeframe for an app review will be 10-14 days for a new app and 5-7 days for a review.
There are times when a developer may wish to remove their binary from the the review queue. This could happen if the binary you submitted has a critical bug which is discovered after submission. Click on the version of the app within ITC. Then you'll see a message in the app's metadata, which has a link to remove your build from the queue (see reference 2).
From the Apple documentation (see reference 1):
If you face extenuating circumstances, you can request the review of your app to be expedited. These circumstances include fixing a critical bug in your app on the App Store or releasing your app to coincide with an event you are directly associated with.
Urgent Bug Fix: If you've submitted an update to fix a critical bug in your app on the App Store and you are requesting an expedited review, be sure to include the steps to reproduce the bug on the current version of your app.
Time-Sensitive Event: For apps associated with an event, we recommend you plan and schedule the release of your app in iTunes Connect. However, if your app is stil in review and the launch of your event is quickly approaching, you can request to have your app review expedited. When submitting your request, it's important to include the event, date of the event, and your app's association with the event.
Please Note: Expedited reviews are granted on a limited basis and we cannot guarantee that every request will be expedited. Sign in to request an expedited review.
If Apple decides to reject your binary upload, they will provide a very specific reason from the following document: https://developer.apple.com/app-store/review/guidelines/
You can then respond to their feedback within a form that they will send to you. Please remember to be courteous and polite to your reviewer. Once you've responded, you can upload a new binary, if necessary. Sometimes, Apple will reject for missing metadata. If this is the case, you can edit the metadata and submit your existing build for review, without uploading a new binary. Apple looks at every build and every comment.
 Apple's App Review Documentation https://developer.apple.com/support/appstore/app-review/
 Viewing and Changing Your App’s Status and Availability https://developer.apple.com/library/ios/documentation/LanguagesUtilities/Conceptual/iTunesConnect_Guide/Chapters/ChangingAppStatus.html