If you have enough of a single fruit to make a full carboy, then I would ferment them separate and blend closer to bottling. If you only have a few pounds of this and that then I guess there’s not much choice but to put it all together. You might find that 25% is the limit where one fruit dominates the blend, you can’t taste anything else. In that case it’s too late to unblend it.
If you don’t harvest enough to make a full batch you could always freeze it and accumulate until you do. That’s an advantage of fruit winemaking. In fact it’s beneficial to freeze the fruit to extract more juice/flavor. You also aren’t tied to the grape season schedule-wise.