Lunaa, take another look at your "timing diagram" pdf, and see if this helps you to work out a method of achieving the goal....
1, 3, 6, 12, 8, 0, 15, 0, 15, 0, 15, 0.
Can you see that those numbers are the decimal representations of the binary patterns formed in the a, b, c, d columns, where a = bit0, b = bit1, etc.
Now think of your "Time" column as a "counted" value, triggered by the elapsed time.
The question doesn't actually state what happens in the time interval from 0 to 1, so I am assuming that time=1 is the 1st period, where your "count" will be 0.
So, time = n, count value = n-1.
I don't know how advanced you are in your education into the world of PLCs, even if you have ever heard of "indirect addressing".
That is the approach I would use if I had to use timers and counters.