In the sgml, second should be plural in 'intead of the number of second since the'. And 'intead' should be 'instead'.
Ok.
--progress-timestamp use a Unix-like epoch timestamp for progress reporting
but that is getting pretty long.
Indeed. I've done:
--progress-timestamp use Unix epoch timestamps in ms for progress
A quibble, but it isn't in ms, it is in seconds. The digits after the decimal point give a precision to the ms level, but they don't change the base unit. I would just leave the units out of the help description, as the progress message itself includes the units.
Since this is mostly bikeshedding, I've marked it ready for committer. Let's see what color they like the shed.