Function known_until 

pub fn known_until(
    due: i64,
    from: i64,
    until: i64,
    record_lost: Option<i64>,
    peers: &[Peer],
) -> i64

Until when a dose due at due, known not taken at from (doubts_now), stays known while nothing new is read (a device in use goes stale after FRESH): the first moment it is not, else until; 0 when it is not known at from. For what is shown ahead of time (a phone’s home screen card).