So you are going to run into a bit of a limitation here. However, I have a suggestion that might work for you, it just won't be pretty.
Since you can have a multi-value facet, why not create a "DateRange" facet that is a date/time. Then for each item, add a value for every day in your date range for that image. So 2010/1/1 - 2010/2/1 should have 32 date values in your facet. You "should"
be able to create a filter off of that facet that will meet your needs.
Let me know if this works for you.
Tony