Fruits staying on the tree has insignificant impact on the productivity of mature grapefruits and pummelos. Definitely my mature ever blooming, ever fruiting Calamondins are not affected at all, it has blooms and fruits of all stages all year.
How long they can stay will depend on cultivar. Ortanique, Gold Nugget Mandarin, most grapefruits and pummelos can stay on the tree for 6 months or more after they attain good flavor for harvesting. And for these good keepers, they usually get better in taste and quality the longer they keep. Thus you can schedule the harvest according to your whims and comfort. In fact the best place to store your fruits are on the tree and not on your fridge, that is why I favor most of the good keeping cultivars. You have beautiful displays of fruits much longer, you get to save space on your fridge, you get that priceless expressions of joys illuminating from the faces of your friends and guests as they pick the fruits for themselves during gatherings or parties in your yard and wonder with astonishment as soon as they taste good quality fruits, and to me I believe is much more important than any miniscule improvement in yields. Moreover, by picking the fruits earlier and depending on cultivar, it could have disadvantages such as crowding in your countertops or fridge, rotting away of the excess harvested fruits, not as good quality compared to picking later (cultivar dependent), not fetching a good price on the fruits by not waiting for optimal price. But of course it depends upon the goals of why we grow citruses. Oftentimes, the goals of a commercial citrus growers have direct contradictions to the goals of a backyard fruit grower. So you will have to keep in mind that most of the recommendations by LSU, UCR, and other scientific research are mostly to help the citrus industry. Thus they are geared towards maximizing yields.