You should be able to get a jewelers loupe for around the 5 dollar mark that will serve you well down the road. These pics seem to be taken with some time in between as the latest set of pics show some maturity of the pistils. The first set of pics showed smaller buds with bleach white pistils standing straight out, some in the second set show maturing pistils and older buds in general.
I haven't gone back up to check, but knowing exactly how many days they've been in flower gives you a starting point. Things that can change that are sudden drastic stress on the plant, lights, water and nutes. I've seen people judge by pistils alone while having fresh pistils on their foxtails and they let it go too far.
Regardless of how large the buds will eventually get you want to chop when the psychoactive part of the plant is ready, and that's your trichomes as most have stated. They are usually the final judge of when to chop because not getting the timing right won't yield the desired results most of the time.
Get a loupe and check all over the plants not just the top buds. Check all buds and sugar leaves you intend to keep in the buds at all heights of the plant. What's on the top buds has a tendency to ripen first. The older trichs will ripen first generally so what you're looking for is the best balance you can get of trichome clear or cloudiness to amber across the entire surface of the plant you intend to consume for the typical THC benefits. If you're looking for couch lock then let most of them all turn amber and then chop and you'll be snoozing in no time.