When track_io_timing is on, I/O timing information is displayed in pg_stat_database, in the output of EXPLAIN when the BUFFERS option is used, and in pg_stat_statements as documented in [1].
This is also described in the manual for pg_stat_statements [2], however, manuals for pg_stat_database and EXPLAIN doesn't refer to it.
I think it'll be better to add descriptions to both of them
