"If we're not seeing any concrete timelines, any concrete deadline in terms of when we'll see this 15 per cent reduction, it's meaningless," said NDP critic Jagmeet Singh.
During a campaign-style event at a home in Brampton, where soaring premiums are a big issue, Premier Kathleen Wynne admitted she can't put a date on the pledge to lower auto insurance rates, or say over what period the rate cut would be averaged.
"I just don't believe that it's possible for us to put a firm date," Wynne said after discussing insurance rates with a local family.
"We've talked to the industry, we understand that it's complex and that there are changes across the system that need to be made, so we have to do this in a prudent way."
The minority Liberal government made the promise to cut auto insurance rates in order to get NDP support for their budget, but vague wording left the New Democrats suspicious of the plan and demanding the cuts be made in one year.
The NDP has been pushing for an across the board cut in auto insurance rates since the government made regulatory changes in 2010 that limited coverage and saved the industry huge amounts of money.
"We've seen three years of $2 billion of annual savings that the insurance companies are enjoying, and none of that being passed on to drivers," added Singh.
"We're confident that given the savings that are already in the system, that the government has the ability to enact changes to get the passing on of those savings within a year."
Wynne couldn't say when the rate cuts would start or if they could be averaged over several years, but said she didn't want to push the industry so hard that it started denying coverage to some drivers.
"What I don't want to do is create a situation where there are people who won't be able to get insurance because the insurance industry says 'you're pushing us too hard, we just won't write insurance for certain parts of the population,'" said Wynne.
"As soon as this budget passes, as soon as we have the opportunity to implement this initiative, we will begin to work on it, and we'll make it happen as quickly as we can."
The Progressive Conservatives have a plan to reduce fraud and increase competition in the auto insurance sector that they said would reduce rates faster than the Liberal or NDP proposals.
"Our plan will start to deliver lower rates in the marketplace far quicker than the plan laid out by the premier and the NDP," said PC critic Jeff Yurek. "It's up to competition, but it might be 10 per cent, 15 per cent it might be 30 per cent."
The New Democrats were set to unveil yet another demand Friday in exchange for supporting the budget, a firm five-day guarantee for seniors needing homecare services.
A frustrated Wynne said the budget was crafted to meet many NDP concerns, and she'd like the New Democrats to just make all their demands at once.
"I believe we have a budget that is a good budget that should be implemented as it stands," she said. "If there are other things that the NDP want to talk about, I don't know the specifics of those right now."