I have never gone over 48 hours but I see no reason why you shouldn't. At that point it is yogurt "cheese".
Some of the whey can be kept to make your next batch. You can also freeze it for future use.
Give the rest to your pigs. They will think they went to piggy heaven.
“Some of the whey can be kept to make your next batch”
I don’t suppose you can make ricotta with it, since it has the yogurt bacteria in it?
No need to buy yogurt starter. Next time you’re cutting up a hot or sweet pepper, freeze the stems and caps. Pull any of the flesh off. Use 6, ymmv, stems and caps per quart of heated/cooled milk product and incubate as usual.
I’ve gone through various methods of incubation and settled on the oven. Heat it on the very lowest temp for 60 seconds and turn off. Put a qt canning jar in without the lid. Turn the oven on the lowest temp. and count to 60 maybe twice and turn it off throughout the incubation. It gels up nicely in 6 hours so less time than other methods I’ve used and has very very little whey. If you need to use the oven, just put the jar back in once it’s cooled down so easy peasy. Regular store bought milk, whipping cream (!), powdered, etc. works.
The first batch will taste slightly of the pepper but the chains will taste like plain yogurt. I like the jalapeno taste over the bell pepper. The first batch can be frozen in ice trays and used as starters so those future batches won’t taste of pepper. Or use that first batch in a veggie dip or drain (very little whey with the oven method) to use as the cream cheese in a savory cheese cake.