I suspect that internally the Chronic_between gem is using the UTC time as opposed to local BST.
Time.now #=> 2012-04-17 09:56:39 +0100
require 'chronic_between'
ChronicBetween.new('8:56-09:00').within? DateTime.now #=> true
DateTime.now #=> #<DateTime: 2012-04-17T10:00:16+01:00 (53050353304023146357/21600000000000,1/24,2299161)>