I would write the rule like we have at our field: no alcohol on field premises at any time. Whatever rule written to permit it under certain circumstances would eventually get bent or have enough "gray" in it that it would be inneffectual
Unfortunately, this is the type of mentality that creates so many problems. "Make a Law", "Make a Law." I can understand some time restraint concerning the use of whatever prior to engaging in some activity be it good or bad.
The "Make it illegal to have whatever for everyone everywhere," is a socialist function that I totally reject be it good or bad. We get more than enough of such garbage in simply living.