With my gas savings, I bought this! (2000 Honda Insight)

[Ecky]

Mine needed more than 24 hours. I left it on a full 2 days, and it seemed to balance it better than any previous grid charge.

[cowmeat]

It's pretty hard to nail down a correct amount of time to keep charging after the voltage tops out, but I ended up leaving it charging for an extra four hours after it topped out at 168. Opinions are all over the board when you read about grid charging and discharging, so I tried to play it safe.
Of course the Hybrid Automotive grid charger only shows full numbers on the readout (which is pretty annoying), so it could have actually been less than four hours overcharging.