I saw WritersCube using a dream clock in his dream journals, and it seems really effective. Few questions
How does this work?
How do you make on in a dream?
How does time go by in a lucid dream? Second by second?
Does this work effectively?
Any answers will be appreciated.
I use somewhat of a same method that WC uses, though i do want to discuss how we streach dream time with him 
but i have an extrememly high-detailed watch that i use to set how many in-dream hours i wish to use, and if i never increase the time is set to 1 hour as an average.
and as you asked for efectiveness, it has worked for me night after night and has always worked just as i set it ^^
as for making one i just kindof imagined that it would be there and there it was 
(sorry if that isnt very helpfull but thats how it first worked for me)