Have you not got the pack they came in?
They really do need to be kept in a sealed container and in date for them to be accurate.
The guage on ketostix goes from a beigy /peach which is negative, through pink to deep purple.
You should also read them dead on 15 seconds but to be honest you can see immediately if they are going to change colour and the amount of keytones isnt important.
As for time of day, I think quite a few people do it first thing, I do but I'm not sure it matters.
Found this image of the ketostix chart although might not be exact due to monitor colour differences