Question 1162938
Having a question might be useful.  One would assume the situation is exponential decay.  You could try using a model like,....  Notice that  40.5  is  {{{1/8}}} of 324.   If you start with  324, then:
<pre>
HALVING
PERIODS     AMOUNT GOO
0            324
1            162
2             81
3             40.5
</pre>

Maybe you can see how to use this pattern.
255 minutes is 3 halving periods.