step 1: a b c x a b c x a b c x a b c x a b c x a b c x a b c x...
step 2:       d       e       f       x       x       x       d...

##</code><code>##

seconds task   
  4     a b c    
 24     d e f  a group of 3 blank slots occur every 24 seconds
               There are 3 categories of other things. 
               Even if they all land on the same 24 second 
               "window", we can still run one of each
               of them. In other words, each of these 3
               slots could be dedicated as 
               "potential 96, 144 or 600 second thing".
 96     g      run once every 4th group
144     h i j  run one of them every other group 
               (pattern repeats after 6 groups)
600     k      run once every 25th group

##</code><code>##

1   a
2   b
3   c
4     d
5   a
6   b
7   c
8    potentially run one of the every 96 second group 
9   a
10  b
11  c
12    e
13  a
14  b
15  c
16   potentially run one of the every 144 second group 
17  a
18  b
19  c
20    f
21  a
22  b
23  c
24   potentially run one of the every 600 second group