Query Workbench 60s timeout - how to extend?

That behavior is not expected. I found instances of 4.5.1 and 4.6.1, and both of them issue the following message after 300 seconds:

{
  "status": "Gateway Timeout",
  "status_detail": "The query workbench only supports queries running for 300 seconds. Use cbq from the command-line for longer running queries. Certain DML queries, such as index creation, will continue in the background despite the user interface timeout."
}

Is that what you are seeing after 60 seconds? Or something else?

This certainly could be worth raising a ticket if we don’t find a work-around for you.