classList.add Как выбрать все элементы?

const block1 = document.getElementsByClassName('test1')[0]; 
const block2 = document.getElementsByClassName('test2')[0]; 
const block3 = document.getElementsByClassName('test3')[0]; 
const block4 = document.getElementsByClassName('test4')[0]; 
const block5 = document.getElementsByClassName('test5')[0]; 
const block6 = document.getElementsByClassName('test6')[0]; 
const block7 = document.getElementsByClassName('test7')[0]; 
const block8 = document.getElementsByClassName('test8')[0]; 
const block9 = document.getElementsByClassName('test9'); 
const block = document.getElementsByClassName('test')[0]; 
calculate_timeout = seconds => { 
    now = new Date(), next = new Date(); 
    next.setSeconds(seconds); 
    if (next.getTime() <= now.getTime()) 
      next.setMinutes(next.getMinutes() + 1); 
    return next.getTime() - now.getTime(); 
  } 
  (function timer_callback() { 
    let now = new Date; 
    if (now.getHours() >= 06 && now.getHours() < 09) { 
      block.classList.add('now'); 
      block9.classList.remove('now'); 
    } 
    if (now.getHours() >= 09 && now.getHours() < 10) { 
      block.classList.remove('now'); 
      block1.classList.add('now'); 
    } 
    if (now.getHours() >= 10 && now.getHours() < 11) { 
      block1.classList.remove('now'); 
      block2.classList.add('now'); 
    } 
    if (now.getHours() >= 11 && now.getHours() < 12) { 
      block2.classList.remove('now'); 
      block3.classList.add('now'); 
    } 
    if (now.getHours() >= 12 && now.getHours() < 13) { 
      block3.classList.remove('now'); 
      block4.classList.add('now'); 
    } 
    if (now.getHours() >= 13 && now.getHours() < 14) { 
      block5.classList.remove('now'); 
      block6.classList.add('now'); 
    } 
    if (now.getHours() >= 14 && now.getHours() < 15) { 
      block6.classList.remove('now'); 
      block7.classList.add('now'); 
    } 
    if (now.getHours() >= 15 && now.getHours() < 16) { 
      block7.classList.remove('now'); 
      block8.classList.add('now'); 
    } 
    if (now.getHours() >= 01 && now.getHours() < 23) { 
      block8.classList.remove('now'); 
      for(var i = 0; i < block9.length; i++){ 
	    block9[i].classList.add('now'); 
      }   
    } 
 
  })();

.test.now { 
  background: green; 
} 
 
.test { 
  background: red; 
} 
 
.test1.now { 
  background: green; 
} 
 
.test1 { 
  background: red; 
} 
 
.test2.now { 
  background: green; 
} 
 
.test2 { 
  background: red; 
} 
 
.test3.now { 
  background: green; 
} 
 
.test3 { 
  background: red; 
} 
 
.test4.now { 
  background: green; 
} 
 
.test4 { 
  background: red; 
} 
 
.test5.now { 
  background: green; 
} 
 
.test5 { 
  background: red; 
} 
 
.test6.now { 
  background: green; 
} 
 
.test6 { 
  background: red; 
} 
 
.test7.now { 
  background: green; 
} 
 
.test7 { 
  background: red; 
} 
 
.test8.now { 
  background: green; 
} 
 
.test8 { 
  background: red; 
} 
 
.test9.now { 
  background: green; 
} 
 
.test9 { 
  background: red; 
}

<div class="test1">9</div> 
<div class="test2">10</div> 
<div class="test3">11</div> 
<div class="test4">12</div> 
<div class="test5">13</div> 
<div class="test6">14</div> 
<div class="test7">15</div> 
<div class="test8">16</div> 
<div class="test9">17</div> 
<div class="test9">17</div> 
<div class="test">test</div>