Alkylation is a general term to describe the transfer of an alkyl group from one molecule to another. It sounds to me as though you are talking specifically about alkylation in reference to petroleum products and production of branched hydrocarbons for high octane fuel products.
I can't claim to be an expert on the oil industry, so I will not just regurgitate wikipedia to you for the answer to your question about the timing of the alkylation process.
...and in fact, I see that the answer to your second question can be found on wiki too:
Cracking and
Catalytic Reforming (which isn't to be confused with Steam reforming, the main production method of syngas (and hydrogen)).