For this question, "maneuver" will designate any maneuver involving a change in $\Delta V$ (either direction, intensity, or both). The maneuver implying rotation only (such as the one the Hubble space telescope perform thanks to its reaction wheels) does not count.
The question arise when I was playing to KSP waiting for a high $\Delta V$ maneuver performe with a low thrust to weight ratio spacecraft to end.
The question "Longest continuous burning chemical rocket engine?" speaks of long burn but is restricted to chemical engines.
Electric propulsion can offer higher ISP but with low thrust. Thus, to perform a maneuver with a specified $\Delta V$, an electric thruster must be running longer than a chemical one. I'm confident this is not a big issue for unmanned spacecraft traveling in the outer solar system.
I fail to find how much time such an engine can run continuously. Yet, such value is a valid on a test-bed or in theory and does not necessarily reflect values used in real flights.
What is the longest maneuver ever performed? What kind of engines (and possibly RCS) did they used for this maneuver? Did those engines run a max thrust? How much time did this maneuver last?
bonus question: what was the $\Delta V$?