move an electric panel
Having recently had my panel (~20 circuits, 150A service) relocated to the opposite side of the wall it was on (though mine went from exterior to interior, along with a panel upgrade), it took the better part of a day for the electrician to get everything unhooked, taken out, the new panel in, and everything reconnected. The power company took their sweet time reconnecting my meter, but the electricians' work was done by mid-afternoon. 

A rough step-by-step of the work involved:


Have the power company disconnect the meter
Label and disconnect all of the circuits in the panel
Prepare the wall where the panel will be moved to
Remove the panel, and install it (or a new panel) in the new location
Feed all the wires through to the new panel
Reconnect all of the circuits
Get it inspected, if needed / desired
Have the power company reconnect the meter
Drywall repair, trim, cabinet, whatever to hide or improve appearance of panel - this is typically not done by the electrician though


Some things can be done in parallel if there are multiple people available, and some things may involve a lot of waiting.

Make sure to check local codes, permitting requirements, etc.

If you're just planning to flip the panel to the other side of the wall, keeping it in the same stud bay, you won't have any issues relating to obstructions, too-short wires, etc so it may be even easier. Everything being interior makes it a bit easier as well.

I'd strongly urge you to consider how much space your existing panel has and whether a bigger (number of circuits and/or max amperage) panel would be useful. Panels are cheap, compared to the cost of upgrading later on, so if you can swing it to get a bigger panel now (and your existing one is close to full), now is the time to do it.