The matchmaker comes any age between 4 (if it's an Oyajitchi) and 9. If you didn't get it today, you'll probably get it tomorrow. If you don't use the matchmaker, you get an oldie and have to mate with another oldie to get a baby; the matchmaker won't come to an oldie.
The matchmaker comes at certain times. The times I have personally seen are 3 and 6 pm. One can set the time to catch her and I've done that numerous times. When she appears, hit the c button to catch her or she will leave.