An hour is insanely long for a single class. Can you provide more of the output? How many mutants were analysed? How many survived? How many had no coverage? How many timeouts were encountered etc etc.
A lot of different factors influence the performance of mutation testing, so it is hard to predict times from simple things like number of lines of code. The following all decrease performance.
* Tests that perform IO (network, file, disk, access dbs etc). These can hang, are generally much slower even when they don't, and can give unpredictable results when run in different orders.
* Code that is covered by tests, but poorly tested. All tests that exercise this code must be executed to determine that the mutants survive. They are therefore more expensive than uncovered mutants (where no tests are run), or mutants that are killed.
* Large classes. Pitest currently doesn't run mutants in the same class in parallel, so analysing thousands of mutants in the same class will be single threaded if only 1 class is analysed.
* Slow tests. A test that takes 2 seconds to run might not normally be a problem, but if that test covers a lot of code pitest might need to run it thousands of times (see 2nd point).
* Imperative code with lots of loop counters. These are prone to generating infinite loops, forcing pitest to time the mutant out. Each time out costs seconds.
1.4.11 is of course also very old. It would be worth re-running with the latest version, there have been numerous performance improvements since 1.4.11 was released.
From the timings you provided, the 19 seconds to build the mutation tests is the bit that includes the time taken to analyse mutants with no test coverage. This is very high (normally it is <1 sec), but your 1 hour 24 minutes is not being spent on uncovered mutants.