Is there a way to use Time#strftime to generate a string that contains
milliseconds, and to do so in such a way that Time.parse understands it?

In other words, a value of ms_format that makes this work:

t_now = Time.at(1125180070.216)
diff = Time.parse(t_now.strftime(ms_format)) - t_now
diff.abs < 0.001 # ==> true

The default format does not represent milliseconds, so the diff can be
up to 1.0:

default_format = "%a %b %d %H:%M:%S %Z %Y"
t_now = Time.at(1125180070.216)
diff = Time.parse(t_now.strftime(default_format)) - t_now
p diff.abs # => 0.216

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407