The current code checks every 5 seconds if the obsolete cleanup run thread should run.
Instead, we should check whenever it was configured to run, for instance, see the sweep server:

        __wt_cond_wait_signal(session, conn->sweep_cond, sweep_interval * WT_MILLION,
          __sweep_server_run_chk, &cv_signalled);

The sweep_interval comes from conn->sweep_interval