Can I hire a MERN developer part-time?

Yes. Part-time MERN engagements start at 40 hours per month minimum at the standard hourly rate ($22/hr for mid-level). Part-time is appropriate for maintenance retainers, post-launch bug fixing, or code review. For ongoing product work with a continuous sprint backlog, full-time dedicated ($3,200/month) is usually better value because there is no scheduling overhead and the engineer builds deeper codebase context.