Or is it December 31?
At what point in the transaction does it count for income purposes? Is it when they issue the check or when the check is received by the Roth IRA?
What about if it's an electronic transfer?
(I am considering doing this but want it to be on my 2016 taxes)
You need to roll it into a tIRA then convert to ROTH IRA and it all needs done before year end. Most 401K don't allow roll overs unless you leave the job. Make sure you understand all the laws before deciding anything. Even your age matters if you are over 55 when you leave your last job you might want to leave in the 401K. If you roll it over you might want to spread the conversation over more than one year to reduce taxes.
No. The year it is taxed is the year the money is posted to your Roth IRA account.
It is December 31.
The date that counts is when it leaves the 401K.
responding again to your post if your income tax liability is going to b $1K or more you need to prepay on 1040ES when you take the distribution
or if not pay by April17, 2017
electronic transfer -the day it's made