According to findings by research psychologist Professor Marissa Harrison, from Pennsylvania State University (in the USA), on average it takes a man about three weeks to “fall in love” whereas it takes a woman about five months.
As she points out, there are exceptions to every rule, but this was the outcome of Professor Harrison’s findings based on interviews with college students over extended periods and through multiple relationships.
Although they fall in love much faster men generally find it harder to express their feelings and open up and ‘confess’ to the woman that they have fallen in love with her. Hence it is often weeks, and possibly months, after they realise they are in love with the girl of their dreams before they can tell her.
A big part of the reason men fall in love more quickly is that initial love for men is mostly visual whereas women tend to be much more pragmatic (her word, not mine—I must look it up).