This is a question that brides ask me all the time (so do their mothers)! This is really up to the bride and groom.
However, the current trend is to cut the cake about 10 to 15 minutes after the toast. This works out great because then the cutting of the cake is an extension of dinner, and this is customary with weddings that the bride and groom are the first to eat a piece of cake!
It is also the trend to pick out a song for the cutting of the cake. We have suggestions on our Music Express facebook page.
In the past, a couple of decades ago the cutting of the cake would occur about 30-45 minutes after dinner and the first dance.
It is really your decision how you would like to handle this.