How to merge data from 2 endoints?

Question

API

here is the test task

the service should receive flights on these two endpoints, merge them, remove duplicates and send them to the client.
Please note that the endpoint is not stable, meaning it can sometimes crash or respond after a few seconds.
The response time of your service should not exceed 1 second.

how to synchronize responses from 2 endpoints to achieve response in 1 second?
Is there any skeleton for such an application? I only have 2 files in my head - index.js with express launch and one file that does all this work functions/get_flights.js

thanks in advance