You may have to wait 'til Tuesday* for the next TV-publicized mass shooting, but it wasn’t twelve hours before the next actual mass-shooting event occured:
1 death and 7 surviving victims of a shooter on 2523 W Broadway, Louisville KY USA 40211, with no arrest shown
Note that the mass shooting in Arkansas is almost a Mass Killing, as a 3rd victim has now died.
In general, there are on average more than one mass shooting every day in America, and often a high number in a day. On the 15th of June, barely a week ago, there were SIX mass shootings - Cincinatti, Southfield MI, Rochester MI, Detroit, RoundRock, Tuskegee - and 4 of the 51 total victims died. SIX MASS SHOOTINGS reported by newsmedia IN A DAY, but the record I think is 8.
Anyway, I just came to say you may not need to wait four days for the next one, that 4 hours is usually plenty. 'Murica.