Function default_minutes 

pub fn default_minutes(
    task: &Task,
    laid: Option<u32>,
    default_estimate: u32,
) -> u32

A block’s length by default, in minutes: what the plan lays for the task (laid: its corrected estimate, less the time spent, with its margins), its margins aside; else its estimate, else default_estimate. By whole five minutes, a quarter of an hour at least.