A client brought us in for what they called a few hours a week on a payment integration. The first month was quiet. Then a provider certificate expired over a weekend, a reconciliation mismatch showed up days later, and a mobile release needed a change to the same flow. Three different roles, and none of them fit inside "a few hours of a backend developer."
None of that was expensive to do, and each item was small. The expensive part was waiting: everything sat until the one person who knew the system had a free evening.
So we stopped selling part-time engagements in hours and started scoping them by role coverage. The written context lives with the whole team, so whoever is free picks it up (backend, QA, DevOps) and nothing queues behind a single calendar. Some months that really is a few hours. The difference is those few hours happen on the day you need them.
If you work with an outside developer today, your project probably just waits out the week they are unavailable.