Depends on what space you have available. If you are strapped for space and are not doing too many screens at once you may want to read on.
You don't actually need a dark room (as in photography) you need a safe light area.
The safe light colour for screen printing is yellow light;and in this environment you should be able to store screens for up to 2 weeks before they 'fog' or start to expose.
Additionally you should know that the emulsion is not sensitive to light while in its wet form.
So you can coat a screen in the kitchen, during the day time and place it in a dark cupboard to dry, at night (or with thick curtains drawn) have a lamp with a yellow bulb, this is now your safe light area. Place your design on the screen, and eighter expose it in the morning sun or on your exposure unit if you have one.
The amount of light the screen printing emulsion needs to start exposing greater than the amount of light photographic papers need to start exposing.
I hope this helps....let me know