Hi,
I never used it, but afaik there is a "-tN" option to /usr/bin/vacation specifying the days between replies.
Default is indeed one week, and with "-t1" you could reduce this to one day.
Some implementations of vacation even support a suffix of "w", "d", "h", "m" or "s" for weeks, days, hours, minutes, seconds (!).
Try it!
wmp