You are welcome!
I wait to see about 2cm of whey on top of the curd and to see that the curd is either pulling away (shrinking) from the sides of the pot and/or to see some cracks on top of the curd. That happens when the pH is down to about the 4.5-4.7 range, no need to check with a meter (aside for keeping production log). That aside, I taste and smell the curd and judge it. I like it to be as tangy as Greek yogurt and in some cases this means very acidic (Sometimes as much as 4.3pH!). If the curd looks and feels at my target but the flavor is not there yet, I will let it ripen even longer.
I recently taught my brother in law how to make Chévre up in Ontario Canada. He could only get this ultra pasteurized crap of a goats milk. I pre-ripened it for a few hours before adding the rennet and even after adding rennet it took 24 more hours (instead of 12-18) to get a set curd, but the flavor was not there at all. I waited for the 48th hour for it to taste right and eventually we were able to get really great Chévre and Crottin out of it.
Traditionally, this cheese is a farmhouse cheese that is made in spare time, in between other tasks. The recipe is liberal and is adjusted to taste and seasonal temperature. Timing can be stretched anywhere from 12 to 48 hours and being a naturally extremely acidic cheese, it isn't crucial if you miss your pH target (unless of course you have a specific product that customers expect to be exactly the same every time around of course).
Drain thoroughly, reduce humidity, tap and turn the daily and don't wrap it - skin slippage issues will be resolved. You can also reduce geo activity by putting less of it, moving it earlier to the fridge or salting it a lot. That will help too. The cave aging should be between 10 to 20 days but continue the aging in the fridge - you want the texture to continue improving while the rind halts its growth (yet not die or recede). Once you master these you will keep doing them over and over because they are so easy and satisfying and you won't have much troubleshooting anymore. You should have it nearly perfected in just a few batches. If you intend on doing lots of them, I recommend you get the book 'The Fabrication of Farmstead Goat Cheese'.