I can't remember ever manually tweaking these sync intervals, so I assume they are all default
Account: Sync Interval / Sync TimeFrame
Main POP3 account: 30 mins / 7 days
Main IMAP account: 5 mins / 30 days
GMAIL account: 5 mins / 3 months
Also have multiple accounts for which I cannot find Sync Intervals/Timeframes: Yahoo, Facebook, Twitter, LinkedIn, a Client's Email Account (which I believe connects to an Exchange Server), as well as other accounts that only appear in the hub (not in Settings) eg WhatsApp & TubeMap,
Does this make any sense to you?