The round BA logo was first introduced in 1948 so most likely from the 50s-60s, the tins were eventually replaced by light green plastic bottles for the outboard oil. Not sure you can pinpoint the exact year however.
Hey Robb, I agree with Paul, there are quite a few versions of the outboard motor oil cans, I currently have 9 different versions right now, from the '50's all the way to 1969, I will get some updated pics soon to show everyone. If you already have done so, check out Alex Callwell's site' www.britishamericanoil.ca has lotsa history on there. Ken.