You should start with the Greeks.
Yes, this is important advice.
Chronology is important in philosophy, every new idea was a response, restatement or advancement on what came before it.
Very few, if any major philosopher, is readable without an understanding of what came before.
If you take shortcuts and skip a few thousand years then you will get lost and not get as much out of it as you otherwise would.
Three months is enough time to give you a very basic overview and understanding of the Greeks. It'll get you up and running.
Also remember to "read around" each author / work and study the cultural and political events, happenings and attitudes of the time (and from previous eras). Also understanding the art of the time helps too. These heavily influence what a philosopher had to write.
It's useful to start off with short summaries of each philosopher to refresh and expand on the knowledge you already have. Penguin has a few useful books of this description and there are plenty of others.
Once you've read some of these move more into depth with specific ancient Greek philosophers (but keep in mind that some of these don't have complete backlogs of material still available, hell some of them only have a few fragments.