In my experience the time for ripening spreads widely from species to species and maybe even breed to breed. Id say in general you will notice it turn a little paler or more yellow and maybe shrinkle a bit... thats the time when they sure are ripe and its going to split any time soon.
You can safely assume the seeds are ripe long before something happens and the orchid then spends time on producing pressure or tension in the pod to make it split.
So yeah I think thats where experience does it, but since you found a way to keep your plants alive and pollinate them I'd just advise on experimenting a bit and maybe keeping track of things on paper. Also consider just leaving one on until it splits, just for the record and experience, also as said, spilled seeds arent wasted just more tricky.
The seeds are very small, just check it out.