If a rocket is 100kg lighter it can carry 100kg more. But what if it was only 100kg lighter starting at the last minute on a 4 minute ascent? How much more could it carry? Would it be as simple as 1minute/4minutes * 100kg so 25kg? Or is there something I'm missing?

If a rocket is 100kg lighter it can carry 100kg more. But what if it was only 100kg lighter starting at the last minute on a 4 minute ascent? How much more could it carry? Would it be as simple as 1minute/4minutes * 100kg so 25kg? Or is there something I'm missing?