A standard residential switchboard upgrade is usually completed within a day, though the exact time depends on the property and scope of work.
Replacing an old switchboard with a modern one, circuit breakers, safety switches, and appropriate labelling, generally takes 4-8 hours for a typical home, including a short, planned power outage while the changeover happens.
Power to the property is off for part of the day while the changeover happens, your electrician will confirm timing so you can plan around it.
You'll receive a compliance certificate confirming the new switchboard meets current safety standards, worth keeping for insurance or future property sale purposes.