gistfile1.rb

# Dont try this at home
require 'relapse'
require 'active_support/all'

def chain_send(obj, *methods)
  methods.flatten.inject(obj) { |o, a| o.send(a) }
end

def parse(match)
  time = chain_send(match[1].to_i, match[2], match[3])

  if match.captures.compact.size > 3
    changes = {}
    hour, portion = match[4].to_i, match[6]
    hour += 12 if portion == 'pm'
    changes[:hour] = hour
    changes[:min] = match[5]
    time = time.change(changes)
  end

  time
end

Relapse.add_handler(
  /(\d+) ((?:week|day|month|year)s?) (ago)\s?(?:at (\d+)(?::(\d+))?(am|pm))?/i,
  proc { |match| parse(match) }
)

Relapse.parse("3 weeks ago at 10:33pm") #=> 2012-10-08 22:33:00 +0100