As Dave correctly says, it was March 1944 that 35 Squadron started flying Lancasters. They received the first ones on 6th March and flew the first ops in them on 15th according to the info in We Act With One Accord by Alan Cooper.
If you can get hold of a copy of We Act With One Accord you might find it quite interesting. It's about 35 Sqdn PFF, much of it being compiled from extracts of info taken from the Squadron ORB's with some added info from interviews with former crew etc. Publisher is J & HK Publishing.