Function bar_countdown 

pub fn bar_countdown(
    open: DateTime<Utc>,
    timeframe: Timeframe,
    now: DateTime<Utc>,
    close: Option<DateTime<Utc>>,
) -> Option<String>

Formats the time left in an open bar, using an exact host or session close when supplied. Without an exact close, calendar months end at the next month’s first day and intraday bars end no later than UTC midnight, as in BarClock. Closed or future bars have no label.