Well in my case, I took FD for POF after getting ITA. However the money was there in my account for more than 6 months. In case of an FD, letter from the bank is important. You really don't have to show any bank statements unless they have asked for it as an additional document but it is better to submit any way since it will save time.In my case, they didn't ask for any. However they have asked for payslips and bank statements of salary account which I didn't submit in the initial application. I had to submit those later.
But at any cost do not use joint account for POF.
In my opinion, the best way is to either transfer the account immediately to your sole account and take an FD of the same, otherwise you might lose out on some interest or transfer the money to your another account and then again retransfer to the account you wish to use for POF.
And in case they asked for further clarifications you will have to provide statements of account from where the funds have been transferred and since it is a joint account suspicion might arise, in that case you will have to provide a gift deed.
Good luck.