Cusps?

When exactly do cusps end and begin? I am wondering if I am a Cancer Leo Cusp. I always thought it extended from July 19-July 24,but a friend of mine claims it is the 18th not the 19th. I am born July 18 and have a few Leo traits,but I am not sure if I am a cusp or not.

Personally I do not really believe in cusps and I have been interested in astrology for many years. Often it seems that people find characteristics in themselves that do not seem to fit with their standard sun-sign description and if they are born within a few days of another sign like to put it down to that, whereas the explanation may lie elsewhere. For example my sister's birthday is 21st July, so she likes to say that she is a Cancer-Leo cusp (presumably meaning that she feels more "fiery" than seems standard for a Cancer) but then as she has the Moon in Aries I think that any "fieriness" would be down to that. At a stretch I myself might even try to claim that I am on a cusp as I was born 28th August, but any "fieriness" with me would be from the fact that I have a Sag ascendant and four planets in fire signs.

It seems to me that there are certain signs that are regarded as "uncool" (especially Cancer and Virgo), and natives of these signs often like to claim that they are on the cusp of another sign if possible. I even found this with the rock singer Willy Deville who I was a fan of back in the Mink Deville days and who I once met many years ago backstage after a Mink Deville gig in London: in those pre-Internet days info was not so easy to come by, and being interested in astrology even back then I asked him what his zodiac sign was and he told me that he was a Leo-Virgo cusp (25th August). However, like me he has (had) Venus in Leo (which I think is very evident in his music), so this may have provided the "fieriness". As a fellow Virgo I identified very much with his music and was very sad when he died a couple of years ago.