Even though "average" is a statistically non-rigorous term, we should be out of the "5-15 second maximum" holding times mentioned by GP by at least one order of magnitude.
It's average as determined by the statistics from my own algorithm's licensees, and from my competitors. I'm sure there are plenty out there that don't fit that mold, but all I can report on is what I see - and those statistics are what I see day in and day out.
Another disclaimer, the markets I'm quoting these averages from are the ES and ZB.
> said Lun, whose computer holds trades for an average of six days