You can reject your first binary and upload the new one. Your position in the review queue will be reset. If you are worried about the release date more than your stability fixes you can just submit the update immediately after it is released to the app store.
App Store Submission Tips
Changing the Status of Your App –
“Developer Rejected” and “Developer
Removed From Sale”Once you have
submitted your binary, iTunes Connect
allows you to manage and edit many
aspects of your application. However,
it’s important to understand the
impact making changes has on your
application, depending on its state.Developer Rejected
If you need to
submit a new binary for your
application prior to it being reviewed
by the App Store Review Team, you can
change the status of your application
to Developer Rejected. To do so, log
in to iTunes Connect, click on the
Manage Your Applications module, then
click the Reject Binary button from
the application summary view.Keep in mind that changing the status
of your application to Developer
Rejected while it is in the review
process removes your application from
the review queue. The review process
will start again from the beginning
once you resubmit your binary.