After the setter has thrown both darts it is considerate game play for both players to agree on where both darts are placed on the board. This should prevent disagreements on whether the scorer was able to score points with his/her darts. However, the various targets a scorer might have available for any given round do not need to be discussed before he/she throws.
Common practice is that a dart must remain on the board for 5 seconds or longer without falling off to be counted. However, players can agree to an alternate standard.