Telecoms company BT launched the UK-wide contest in August to mark the 80th anniversary of the telephone service, which receives 12 million calls a year.
Verity Giles, 37, hoped to become only the fifth person to give the time "at the third stroke" when people dial 123.
But fellow finalist Alan Steadman, 69, from Dundee, won the competition.
Ms Giles said she was inspired to enter because of her five-year-old daughter, who wanted to take part but fell short of the competition's minimum age limit of 10 years old.
"I found out in September that I'd made it through. I've had to keep it a secret so it's been a long wait for this day," Ms Giles, a recruitment company business manager, said.
Crea Barton, a 20-year-old student from Bangor in County Down was the third finalist.
They were invited to the BT Tower in London where they each recorded the speaking clock script.
"It has been a great experience, not many people can say they have done this can they?" Ms Giles added.
The winner's voice went live during The One Show on Wednesday at 19:00 GMT.
Sara Mendes da Costa has been the voice of the speaking clock since winning the last competition in 2007.
BT has donated 10p to the BBC's Children in Need 2016 from each call from the start of the competition in August until tonight's announcement.
A woman from Bridgend made the final three in a competition to find the new voice of the speaking clock.