Indoor Cat--when to start flea control?

I'm posting here at DU because I have gotten good information about how different pets react to different products. I have decided on Advantage as my flea control product because it worked last year for a bad flea problem with the minimum of extra chemicals not needed for indoor cats.

Now, I have a 10 year old indoor cat that had a terrible flea problem last year for the first time. My vet has said he has seen a flea or two in the past but I chalk that up to being in his waiting room. Last year was the first time I had a major problem with fleas in my home. My cat "escapes" a few times a year but only for an hour or so before a little coaxing gets him back inside. He has not escaped this year.

My question is when is the best time to start flea control? I want to do as little as possible, for chemical reasons, but don't want things to get out of control like last year. I live in the Philadelphia area. I had noticed a few bumps around my cats neck around May last year which I later realized was from scratching that area. By the end of June I knew he had terrible fleas and started treating with Advantage. It took six weeks or more to get rid of all the fleas hatching in the house. I don't want to wait that long but don't want to over-treat. I see no evidence of scratching this year.

So, I've watched very carefully for changes in scratching this year but see none. Should I start treating soon or wait till I see differences in his behavior? Of course, I will start treating if I see a lot of scratching but I don't know if I should treat proactively.

Any Advantage users that have advice about starting before rather than after any evidence of fleas?

Thanks for any advice or antidotes. :)

until fall. My neighbor has an indoor cat that never gets outside, but he has fleas. She thinks that probably when she is outside working in her garden, she brings them in with her.