When artist has begin and end date set to the same year (with no months and days), then it's shown as lasting "0 days". Should be something like "A few months", "Under a year" or "1 year or less" imo.

Some examples (http://musicbrainz.org/search?query=begin:2010+AND+end:2010&type=artist&advanced=1)
http://musicbrainz.org/artist/4e9c81e5-30e9-44ab-8b85-950d83b80df3
http://musicbrainz.org/artist/785e1c02-f535-4fc0-a1d6-23de849ebdcb
http://musicbrainz.org/artist/8205c65a-8c87-4a4b-91e2-b63861283d41
http://musicbrainz.org/artist/d79e9c45-cc83-48f9-a8d1-16b6e74a65e6