Is there any research that shows how long a user is willing to wait for search results to come back before they give up? I know Google has made searching instantaneous for people, but barring general web search, for an app—say, an iOS app with potentially intermittent network connectivity—are there any metrics to show how long is "too long" for a search? I should stress that the kind of search I'm talking about involves communicating with a network service.
If your app is making large queries, and there's a delay or throttling, you may not have control over that. Add to that latency of the network, and your results will take even longer.
What you do have some control over is how responsive your app feels to users, which can buy you some time and forgiveness. Without knowing your situation, is it possible to use some hint text to set user expectations?
There is a distinction between absolute response times, and perceived responsiveness of your app itself.
In the book 'Designing with the Mind in Mind' (Jeff Johnson), one principle is:
Acknowledge user actions instantly, even if returning the answer will take time; preserve users’ perception of cause and effect