There is an admin report for “time to first response”.
And there are also lots of other queries in Data & reporting
Topics stats of Solved/Unsolved topics, inc. 'time to solution' is one you might be interested in. But I think it needs an update to reflect the changes on the solution plugin made in spring. Time to first response by group members and Solved Topic and Moderator Response Stats by Category might also be interesting.
ask.discourse.org is also very good at helping you to write queries that return the data you need