Should we use Instant here?

[olexiyb]

/// Returns the system start date
pub fn start_date(&self) -> &DateTime<Utc> {
    &self.proto.started_at
}

/// Returns the number of seconds since the system started
pub fn uptime(&self) -> u64 {
    let now = Utc::now();
    now.time()
        .signed_duration_since(self.start_date().time())
        .num_seconds() as u64
}