For V1 - V4.5: The matchmaker visiting times are 10:30 AM, 3:00 PM, and 7:00 PM. She will visit at these times for three days, begining a couple of days after your Tamagotchi becomes an adult.
For V5: the matchmaker doesn't come. You have to visit her on the dating channel. You can use the dating channel up to three times a day, after your characters have been adults for 48 unpaused hours.