Sorry, we can only provide 6 choices (1min, 5min, 10min, 30min, 1hr, 1day) for now.
If you have requests on more choices, please send your request by feedback.
New choices for time of tweets to be deleted may be added if we receive many requests. 

You can't cancel any tweets to be deleted once you have set.

There is no limit to set tweets to be deleted.

If you are still authorizing  “app permission” with your tweet account after unsubscribing paid features, the tweet  to be deleted you set
while you were still subscribed will be effective.

Yes.  You can use multiple twitter accounts with one subscription, but you can only use one twitter account per one Apple account.You can post from different twitter accounts by logging out each time you change accounts.Even if you log out from the APP, tweets will be deleted once it is set.Also, if you are subscribing paid features, you will not be charged for more than one subscription, even if you use multiple twitter accounts. 

You can use paid features on multiple iOS devices with same Apple account, but you can only use 1 device at the same time.
If you use paid features on other iOS devices, paid features will be ineffective automatically those iOS devices. 
You can restart paid features when you "restore" the subscription.
Also, if you still subscribe paid features, you will not be charged for more than one subscription even if you use multiple iOS devices.

Sorry, subscriptions are managed by each Apple accounts, so you need to subscribe by each Apple account.

1: Select “Settings”
app> “Username”> “Subscription” on your iOS device.

2: Tap “ephemera” from
the list of subscriptions.

3: Tap “Cancel
subscription” to cancel. If you do not see "Cancel subscription", you have already canceled (and therefore will not be renewed).