if(AND(HOUR(NOW())>8,HOUR(NOW())<20),"TODAY() 08:00:00",IF(HOUR(NOW())>=20,"TODAY() 20:00:00","TODAY()-1 20:00:00"))
if(AND(HOUR(NOW())>8,HOUR(NOW())<20),CONCATENATE(TODAY()," 08:00:00"),IF(HOUR(NOW())>=20,CONCATENATE(TODAY()," 20:00:00"),CONCATENATE(TODAY()-1," 20:00:00")))