It's a simple little plugin that counts years, months, days, hours, minutes, seconds between the date you set in the widget parameters and now. If you leave the "time" setting at 00:00:00 it counts in years and months and days. It counts up from a past date, or down to a future date. You get to pick the title for the widget, the text for before the count, and the text for after the count.
Pretty simple yah?
I think technically it is possible for it to say "1 year 12 months 4 days" because it assumes 365 days is a year and 30 days is a month, but so what: it'll only be funky like that for about 4 days yah?