Are you ready to deliver?

I don't think this situation is different from others. There is a business who wants a solution, there is a manager who needs the business having this solution, there is another manager who is responsible to get the good solution in production, there are business users who are made responsible for test execution and there is you. You are responsible for the test process.

What are you going to do when the solution must be tonight in production?

Some people are spending time to identify the possible risks. Others spend time to convince certain managers that it won't happen. Perhaps there are testers who just start testing.

I'm sure that all situations will fail. Normally we start identifying risks related to what should not happen in production and we will try to measure that those situations will not occur. This process of identification takes too much time of the 4 hours you have left. You will have the risk identified and just a couple of hours to check if those risks are covered. And afterwards you didn't fill in the complete picture although you created the expectation that after testing all risks are measured and identified.

Convincing the managers that you are not able to test would another approach. Only this will not help the business.

Start testing saves some time, only how will you know you did the right thing?

A previous test manager of mine told me that if business is not able to tell what should work or what risk should be avoided, ask them which errors they don't want to see.

I can imagine that you identify together with the business what value the new solution will have.
For example:
- The new screen enables the user to approach information faster which helps the user the process the customer information easier and therefore the service level increases.

I can imagine that translating this into errors the business wouldn't like is hard. You might enter the zone of negative testing.
You might start with the primary functions in the process like:
- Printing an annual bill;
- Sending a confirmation letter;
- Correct storage of data;
- ...

You might think of all kinds of variations of printing a bill. What about proofing that the user is able to print the annual bill for that client and is not able to disturb printing using that screen for other clients?

This could be translated in errors to avoid.
I don't want to see that:
- The annual bill for this group of clients is not printed
- The confirmation letters are sent more then 1 time
- The confirmation letter is send to incorrect people
- The data which is changed or created cannot be seen after returning after a next login
- The user spend more time to identify what is happening on the new screen

Will this avoid all risks? I don't think so. Will this help? I believe so as you minimized the number of test cases just by defining together with the business what should not happen. I strongly believe that in a half an hour discussion the business can tell you which disasters should not happen as they already have experience with it. It will be harder to identify all items which should work.

Will this lead to a solid advice on quality? Sure it will not. It will give the business an indication about the quality. If you tell them you are not able to cover all points within the given timeframe to make a solid advice but you might give them indication what might happen and based on what this indication is made, they might be able to accept this approach. And afterwards they are able to tell if they will accept the risks when you are finished. This might lead to a situation were you are finished within time and the business has tghere solution.

I suggest that a quick action force is available when things are put into production and monitoring if the errors defined are not happening.