A cancellation at nine the night before is a scheduling event. The same cancellation at seven in the morning is a routing event, and they are not the same problem.
Why it matters
Late notice leaves a shaped hole — a specific hour, in a specific part of the map. Anything that fills it has to be nearby and flexible, which usually means nothing is. The technician absorbs it as unpaid slack, or the office fills it with a stop pulled forward from tomorrow, which moves the problem rather than solving it.
How you notice it slipping
Cancellations are counted as a customer-service number but never as a route number. The same accounts cancel repeatedly without anyone changing their lane. Nothing is in place to fill the gap, so it is filled by whoever happens to shout loudest that morning.
What to do
Track the rate by account, not just overall. Repeat cancellers usually have a structural reason — the wrong day, the wrong time, nobody home — and moving them is cheaper than absorbing it twelve times a year. For the rest, keep a short list of nearby work that could move forward, so a gap has somewhere to go.