I have read that some Mazers never let fruit sit in their fermenting wine or mead for more than two weeks while others will leave the cap for the entire time. Is there any measured science behind the optimal amount of time to leave fruit in for taste or fermentation?
On the safe side I have always ensured that I remove the fruit after around a week.
If its a fruit that I want to ensure I get a lot of flavor out of I would make sure its chopped up and mashed.
If its a really easy fruit to go bad I would suggest added Campden tablets to the must, this will lower the risk of it turning bad.
You could always try removing the fruit after a week or so, and replace it with more. However if this is a high sugar fruit it will make your wine/cider stronger. And for normal yeast you will reach a point of around 18% where no more alcohol will be produced.
You could infuse it with the fruit. in a similar way people age cider in whiskey barrels.