console

2.0.0-p247 :019 > m1 = Movie.create start_time: Time.parse("10:00"), end_time: Time.parse("10:30")
   (0.1ms)  begin transaction
  Movie Load (0.2ms)  SELECT "movies".* FROM "movies"
  SQL (0.8ms)  INSERT INTO "movies" ("created_at", "end_time", "start_time", "updated_at") VALUES (?, ?, ?, ?)  [["created_at", Tue, 22 Oct 2013 14:00:43 UTC +00:00], ["end_time", 2013-10-22 10:30:00 +0200], ["start_time", 2013-10-22 10:00:00 +0200], ["updated_at", Tue, 22 Oct 2013 14:00:43 UTC +00:00]]
   (20.2ms)  commit transaction
 => #<Movie id: 7, start_time: "2013-10-22 10:00:00", end_time: "2013-10-22 10:30:00", created_at: "2013-10-22 14:00:43", updated_at: "2013-10-22 14:00:43"> 
2.0.0-p247 :020 > m2 = Movie.new start_time: Time.parse("10:25"), end_time: Time.parse("10:35")
 => #<Movie id: nil, start_time: "2013-10-22 10:25:00", end_time: "2013-10-22 10:35:00", created_at: nil, updated_at: nil> 
2.0.0-p247 :021 > m2.valid?
  Movie Load (0.3ms)  SELECT "movies".* FROM "movies"
 => true 
2.0.0-p247 :022 > m1 = Movie.first
  Movie Load (0.3ms)  SELECT "movies".* FROM "movies" ORDER BY "movies"."id" ASC LIMIT 1
 => #<Movie id: 7, start_time: "2000-01-01 08:00:00", end_time: "2000-01-01 08:30:00", created_at: "2013-10-22 14:00:43", updated_at: "2013-10-22 14:00:43"> 
2.0.0-p247 :023 > m2.start_time - m1.end_time
 => 435714900.0 
2.0.0-p247 :024 > m1.start_time - m2.end_time
 => -435717300.0 
2.0.0-p247 :025 > m2.save
   (0.1ms)  begin transaction
  Movie Load (0.2ms)  SELECT "movies".* FROM "movies"
  SQL (1.5ms)  INSERT INTO "movies" ("created_at", "end_time", "start_time", "updated_at") VALUES (?, ?, ?, ?)  [["created_at", Tue, 22 Oct 2013 14:02:10 UTC +00:00], ["end_time", 2013-10-22 10:35:00 +0200], ["start_time", 2013-10-22 10:25:00 +0200], ["updated_at", Tue, 22 Oct 2013 14:02:10 UTC +00:00]]
   (57.6ms)  commit transaction
 => true 
2.0.0-p247 :026 > m2.start_time - m1.end_time
 => 435714900.0 
2.0.0-p247 :027 > m1.reload
  Movie Load (0.3ms)  SELECT "movies".* FROM "movies" WHERE "movies"."id" = ? LIMIT 1  [["id", 7]]
 => #<Movie id: 7, start_time: "2000-01-01 08:00:00", end_time: "2000-01-01 08:30:00", created_at: "2013-10-22 14:00:43", updated_at: "2013-10-22 14:00:43"> 
2.0.0-p247 :028 > m2.reload
  Movie Load (0.2ms)  SELECT "movies".* FROM "movies" WHERE "movies"."id" = ? LIMIT 1  [["id", 8]]
 => #<Movie id: 8, start_time: "2000-01-01 08:25:00", end_time: "2000-01-01 08:35:00", created_at: "2013-10-22 14:02:10", updated_at: "2013-10-22 14:02:10"> 
2.0.0-p247 :029 > m2.start_time - m1.end_time
 => -300.0 

controller.rb

def upload
		Movie.delete_all
		xml = params[:upload]
		xml = Nokogiri::XML(xml){ |cfg| cfg.noblanks } # parse xml ignoring whitespace
		xml.xpath('//movie').each do | movie |
			Movie.from_xml(movie).save
		end
		redirect_to timetable_path
	end

Movi.rb

class Movie < ActiveRecord::Base
	belongs_to :channel
	validate :does_not_overlap, :valid_times

	def self.from_xml(xml)
		id = xml.attr('id') #parse movie id
		channel = Channel.find_by_codename(xml.child.name) #get the channel from db
		name = xml.child.xpath('name').text #get name
		start_time = parse_time(xml.child.xpath('start_time').text)
		end_time = parse_time(xml.child.xpath('end_time').text)
		
		new ( {id: id, channel: channel, name: name, start_time: start_time, end_time: end_time, recording: false })
	end

	def valid_times
		if start_time >= end_time
			errors.add(:end_time, "Movie with id #{id} end_time must be posterior to start_time")
		end
	end

	def does_not_overlap
		channel.movies.each do |movie|
			#this trick covers both partial overlaps AND complete enclosings
			if (start_time - movie.end_time) * (movie.start_time - end_time) >= 0 
				errors.add(:end_time, "Movie with id #{id} overlaps with movie with id #{movie.id}")
			end
		end
	end

	private

	def self.parse_time time
		time.gsub!(/\./,':') #replace dot separators by colon as required by Time.parse
		Time.parse(time)
	end
end

xml.xml

<?xml version="1.0" ?>
<movie_data>
	<movie id="1">
		<first_channel>
			<name>Movie1</name>
			<start_time>9.00am</start_time>
			<end_time>10.05am</end_time>
		</first_channel>
	</movie>
	<movie id="3">
		<first_channel>
			<name>Movie2</name>
			<start_time>10.00am</start_time>
			<end_time>11.30am</end_time>
		</first_channel>
	</movie>
</movie_data>