1) If you're using the website, the episodes that are locked will have a lock on the side when you look at the episode list (located on the left), likewise the ones that are unlocked won't have a lock.
Now if you are using the app, the ones that are unlocked will have an arrow on the side for downloading, and the ones that don't means its locked.
2) You can't tell when the key for the Wait-or-pay comics are released on the site. But on the app, there would be a countdown timer for each key. Since the update, the app will also list and tell you when a key is ready/finished waiting.
3) "Read this ep for FREE on iOS/Android!" just means that specific comic is part of the monthly Wait-or-pay, it doesn't mean the entire comic is unlocked on the app.
So for the Wait-or-pay system, you wait a specific amount of time (ex. 24hrs, 2 days, 3 days, 7 days) for a key to unlock AN EPISODE. It doesn't auto-unlock an episode for you. Once you finish waiting for a key, you need to press which episode you want to unlock. That's why when you pressed on a random episode after you finished waiting for the key, you ended up using the key.
Also since they changed the Wait-or-pay feature, you cannot unlock the last couple of episodes using "Wait-or-pay". You have to buy the keys for the last couple episodes (this only applies to the finished comics though, not the ongoing ones)
Hope this answers most of your questions. I don't use an iPhone so I don't know if it's any different, but I'm pretty sure it's the same.
