Besides, he said, viewers accustomed to Jay Leno as host for 17 years, and those who watched Johnny Carson holding court for 30 years before that, need time to warm up to a new guy.
That would be the lanky fellow, formerly of New York, who sports a red pompadour and intriguingly off-kilter comic sensibility.
"My hope is that people will watch the first night and say, 'Hey, there was some fun stuff in there and he cleans up nice. I might try him tomorrow night,'" O'Brien said.
He's far from unprepared. There was a five-year waiting period to claim ownership of "Tonight" after NBC announced the plum job would go to O'Brien, and he's ready for his transition from the 12:30 a.m. "Late Night" to the 11:30 p.m. "Tonight."
He played a different "Tonight" role Friday, as Leno's last guest. O'Brien told the outgoing host he was leaving big shoes to fill.
"You were the only choice. You were the perfect choice," Leno said in return.
A new competitor, Stephen Colbert, also complimented O'Brien.
"He'll be funny and he'll be great. I have tremendous respect for him," said Colbert, whose "The Colbert Report" on Comedy Central airs at the same time as "Tonight."
O'Brien, a former TV writer ("The Simpsons," "Saturday Night Live"), was a raw, largely untested performer when he started with "Late Night." Sixteen years later, he knows how to work the room, including the big one represented by "Tonight."
A test run was encouraging, O'Brien said Thursday.
"We got an audience in and did a show start to finish, and it felt really good," he said. "It was like we built a brand-new ocean liner and last night took it out on the bay, and it didn't blow up. So that's a good sign.
"We were done and I thought, 'We can air that.' It felt pretty good."
Details of the show's look, its rhythm and comedy fixtures will be unveiled next week, but there are clear indications that "Late Night" fans won't be dismayed by an extreme O'Brien makeover.
As an NBC ad summed it up, "New time. Same hair." The host's own assessment is more thoughtful but not far afield of the snappy line.
The theater built for O'Brien on the Universal City studio lot is more "elegant" than his old Studio 6A quarters and, at 380 seats, nearly double the size, O'Brien said. But he's the same comedian and host.
"Comedy is quirky, it's hard, it's very personal. Most of the best things I've done in my life, my comedy career, I just did them and I didn't think about them too much. ... I don't sit around a lot and make diagrams of how I need to alter my personality for 11:30. In fact, I don't think that's really possible."
He acknowledges there are small adjustments to be made as he shifts to "Tonight," comparing it to walking into a party and taking the temperature of the room: How are people dressed? What's the vibe?
