"We do have a timeline. I think everyone realizes for the year of 2017 we're not going to be pulling the rug out from anyone," the New York Republican told CNN's Chris Cuomo on "New Day." "People need not worry that sometime in March or April they're going to lose their insurance plan."
Although parts of the Affordable Care Act could be repealed within the first 100 days, that would not have an immediate impact on Americans relying on the coverage, he said.
"I believe the plans that people are now signing up for will be their insurance plans for 2017. There's nothing we can do today that would impact that," Collins said.
The co-chairman of the Trump campaign's House Leadership Committee said some parts of Obamacare will remain in place.
"We're going to keep the 25 and younger on the family plan, so people don't need to worry about that. There's a lot of details to work out," Collins said.
Collins acknowledged that repealing all of Obamacare immediately would be a challenge for Republicans. "I don't think the Democrats are going to allow us to just repeal it -- they would filibuster that." Collins said.
But the administration still has big plans for change in the first 100 days.
"The first move is going to be signing and repealing or undoing many of the executive orders," Collins said. "That can be done extraordinarily quickly."
But ultimately the changes will take significant time, he said.
"We have replacement ideas. We're going to have to make sure we run that through the administration. That's going to take longer. Lets' face it. It'll be a transition," Collins said. "You don't cut it off on a Tuesday and on Wednesday say here's a new plan."
Among the Obamacare provisions that Congress could repeal are the mandates that individuals have coverage and that companies with 50 or more employees provide workers with affordable insurance. Also, lawmakers could do away with the federal subsidies by 2018, eliminate funding for Medicaid expansion, and cancel a multitude of Obamacare-related taxes.