PORTLAND – The rail authority that runs Amtrak’s Downeaster passenger rail service is making changes to its weekend schedule so visitors can stay in Maine longer.

Starting Saturday, the last Boston-bound train out of Portland will depart at 7 p.m., rather than 4 p.m. The current schedule will remain in effect Monday through Friday.

Previously, day-trippers from the south could spend 31/2-hours in Portland before having to catch a train home. Now, they’ll be able to spend 61/2 hours in Maine’s largest city.

Local merchants are applauding the development.

Not only will people stay longer and spend more money, they say, but the new schedule will lure more people to the area from Boston and coastal New Hampshire.

“I’m very excited about the possibility to have three extra hours,” said Barbara Whitten, president of the Convention and Visitors Bureau of Greater Portland. “It gives visitors a chance to see a couple of museums and historic homes, do more shopping and possibly have dinner.”

Jane Garvin would have liked such an opportunity this week. She and her three friends would have visited Victoria Mansion and dined in the Old Port Thursday if they had time. But as it was, they had to catch the 4 p.m. train back to Wells.

Changing the schedule was not a simple matter.

Much of the Downeaster’s journey is on a single track that is shared with freight trains.

It’s like a one-way street, said Patricia Douglas, the Northern New England Passenger Rail Authority’s manager of planning and development.

Moving the 4 p.m. train to 7 p.m. required other changes to the schedule.

On Saturday and Sunday, the 6:05 a.m. train out of Portland will leave 25 minutes later and the 6:15 p.m. northbound train out of Boston will be pushed back to 7:45 p.m.

When the train service began last December, it gave an immediate boost to downtown merchants and Whitten called the train a blessing for the summer season. The service is used more by Mainers heading toward Boston than vice versa, however.

A survey in May found that 45 percent of riders were from Maine, 24 percent from Massachusetts and 24 percent New Hampshire.