Customize Mongoid to persist times as integers +/- epoch.

time.rb

module Windows
  class Time
    include Mongoid::Fields::Serializable

    def deserialize(time)
      Time.at(time)
    end

    def serialize(time)
      time.to_i
    end
  end
end

class Foo
  include Mongoid::Document
  field :time, type: Windows::Time
end

You will see when you save, Mongoid will store in seconds pre or post epoch:

Foo.create(time: Time.now)
#=> MONGODB mongoid_sandbox['foos'].insert([{"time"=>1324481141, "_id"=>BSON::ObjectId('4ef1fa758ad548115a000001')}])
Foo.create(time: 50.years.ago)
#=> MONGODB mongoid_sandbox['foos'].insert([{"time"=>-253355659, "_id"=>BSON::ObjectId('4ef1fa758ad548115a000002')}])

And when you query, Mongoid will convert as well:

Foo.where(:time.gt => 30.years.ago).to_a
#=> MONGODB mongoid_sandbox['foos'].find({:time=>{"$gt"=>377796341}})
#=> [#<Foo _id: 4ef1fa758ad548115a000001, _type: nil, time: 1324481141>]

Foo.where(:time.lt => 30.years.ago).to_a
#=> MONGODB mongoid_sandbox['foos'].find({:time=>{"$lt"=>377796341}})
#=> [#<Foo _id: 4ef1fa758ad548115a000002, _type: nil, time: -253355659>]