Promote internally or hire from outside?
Internal promotions keep culture. Outside hires bring new ideas. Pick the right one for the role.
Promote when behavior is already there
If someone on the team is already informally leading, the promotion is just paperwork. That's the right time.
Hire outside when the gap is skill, not behavior
A new specialty, a system you don't have, an experience the shop has never been through: that's an outside hire. Internal will struggle to lead something the shop has never done.
Either way, set 90-day expectations in writing
Both internal and external hires fail when the first 90 days are vague. Write down what success looks like before the start date.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.