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 of 324. If you start with 324, then:
HALVING
PERIODS AMOUNT GOO
0 324
1 162
2 81
3 40.5
Maybe you can see how to use this pattern.
255 minutes is 3 halving periods.