You should be perfectly fine overnight on 2x if the villagers have all of their necessities. This wouldn't be recommended for anyone who does not have at least level 2 farming though as those villagers seem to pick berries double time when you're not looking.
However, I personally wouldn't recommend leaving your villagers on 2x for long extended periods of time without checking them. I made that mistake, left with 90 villagers, went out of town for work, supposed to be back that night, got caught out of town for two more days unexpectedly, came back to measles and 18 villagers!!! Should have put them on half speed.
Crazy little guys got busy though and I was back up to 90 in a day and half.... lol

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My VV2 story, "A Twist of Fate" And don't miss Krystal's stories, all three of them!
"Life is too fast... unless you're in traffic."