Apple's app review process can take anywhere from 1-12 days. If timing of your app release is a concern, Apple offers an "expedited" app review, which you can request by logging in to the iTunes connect service.
After you logged in, you need to click on the Contact us button inside the iTunes connect interface.
After the Contact form interface opens, you need to select the following.
Topic 1: App review
Topic 2: Request Expedited review
After this, you should see a link called Request an Expedited App review.
We recommend making sure your app is a complete as possible, including your "Design", "Publish Info" and "Content" elements. Apple provides key information on their review process as part of there App Store Review Guidelines.
Google's app review process can take anywhere from 1-3 days, but is usually in the store within 24 hours of submission.