Normally how long do European people learn how to speak another European language? It is taking me ages to learn some German.
Italian is super easy if you have a French or Spanish background.
And Spanish is super easy if you have Italian or Portuguese background.
Portuguese can be learnt from Spanish easily.
French can be learnt from Italian easily.
English is probably the easiest Germanic language to learn, so anyone with that background can learn it faster.
And Germanic languages between them have similarities but also some awkward differences so it depends on what you're trying to cross.
The more languages you speak, the easier it is to pick another one up.
The difficulties arise when you want to learn a language based on a different alphabet.
And from a different language family.
Then the other issue is learning the proper language versus speech. For example lots of Serbs, Russians, Romanians, Bulgarians and Poles can learn to speak Greek, but not exactly proper and not easy at all to read and write. They can still communicate though, to an almost fluent level. Vice versa it's almost impossible to the same degree. So it also depends on the language itself. Greek is easily spoken and you can violate grammar and pronunciation all you want and people will still understand you. With native English speakers, you'll definitely lose them if your "bus" and "bass" sounds the same, which I've always found hilarious.
Bisseck is a native French speaker, so learning Italian should be easy for him.
In terms of timing, I'd argue that 2-3 months of intense learning is enough for a French speaker to get to a good level of Italian. After 1-2 years he'd definitely be able to be fluent.