There is no industry standard that calls for the maximum length of 1/4" tubing connecting 1/2" tubing header.
However, you do not want to go too long, e.g. 8 to 10 feet of tubing without instrument as it may loose the air pressure needed for a particular instrument that requires air.
Hope that gives you an answer. If more is needed, please elaborate your question so I can provide exactly what you are looking for.