I was doing range queries in the Search Center UI to limit documents between two exact dates.

But no matter what I entered as hours/minutes/seconds in my query I still got the same result.

There are good and bad news around this. The good news is that you can change the resolution from day to for example hours for your default rank profile:

$rank = Get-FASTSearchMetadataRankProfile
$rank.FreshnessResolution = “Hour”
$rank.Update()

The bad news is that the Search Center UI disregards this, and when monitoring the queries received by FAST all hours/minutes/seconds are stripped from the query. They are adjusted for time zones as you can see below where 00:00:00 is turned into 23:00:00 of the day before the original query.

If you want to do date range queries on an interval less than a day you have to use the development API’s, and not the default Search page.