Simplistic Lava Lamp
Python 2, 117 113 108 107 106 105 bytes



from random import*
def f(n):a=['']*5;exec"i=randint(0,(n&gt;44)+(n&gt;59)&lt;&lt;1);a[i]=(a[i]or 0)+1;"*1000;print a


Try it online!

Returns a reversed list (bottom first)



Version inspired by the stackoverflow answer in the comments (edgecases are more likely):

Python 2, 129 bytes



from random import*
def f(n):a=sorted([1000]*5+sample(range(1001)*5,(n&gt;44)+(n&gt;59)&lt;&lt;1));print[y-x or''for x,y in zip([0]+a,a)[:5]]


Try it online!