I'd like to know if a bag-in-box white wine can be maintained outside the fridge and for how long.
Yes, it can. Once opened, the box should stay fresh for roughly six weeks. Estimates differ, but that's the assertion made by one of the leading producers of bag-in-box packaging. Most consumers are familiar with the packaging, though it's not as prevalent here as in, say, Australia. Inside the box is a plastic bladder containing anywhere from 1 1/2 to several litres of wine. The bag comes with a spout that protrudes out from the base of the box and is designed to extend over the edge of a kitchen counter or fridge shelf for easy pouring.
Bag-in-box saves on packaging and shipping costs, but the big benefit for consumers is convenience. As you pour, the bladder collapses inside the box, leaving no residual air to oxidize – or spoil – the wine. But the seal is not perfect; traces of air permeate through the spout, and within about six weeks the wine will begin to significantly lose freshness. (Until the spout is breached, a bag can stay fresh for several months, and some wineries include recommended best-before dates on their boxes.)
As with all wine, bag-in-box products last longer in the fridge (whether it's a white or a red) simply because cool temperatures slow down the chemical reactions associated with spoilage. But the big enemy with wine is oxygen, and bag-in-box provides a pretty good barrier against it, so it's not crucial that you store your white boxed wine in the fridge. Unless, of course, you want to hide the box from your guests.