Gallagher said another reason for the two-year gestation period was the fact that she had been "very shy".
"We'd both been writing music on our own, but we'd never crossed that bridge of doing it together," Gallagher said.
"It took a while to get comfortable."
Gallagher said recording "In Transit" in a remote part of the country had given the pair a break from the hectic pace of the capital.
"Up until that point it had been five years of pretty full-on jobs, and university before that. It's the first time either of us have really had time to focus on music and reworking our values.
"Some of the songs towards the end of the album capture the ambience of where we were."
Their stay in Delaware Bay had been the first time the pair were "fully in a place that amazed" them, Gallagher said.
"The album itself is very much speaking about the experience of this year, and how it's been a really amazing time for us. I'm sure we're not alone in that.
"It's criticising the pace that we do live our lives at, and that constant state of motion. What are your values when all that comes to a halt and you're forced to have a broader perspective on things around you?"
Gallagher and Bartley are joined on record and on the road by drummer Josh Brown and bass player Hugo Olsen-Smith. While only Gallagher and Bartley were in Delaware Bay during the recording of "In Transit", the rhythm section duo were able to track their parts separately and send them south.
"They self-recorded all their parts for the album in Wellington on their own little home setups," Bartley said.
"They had demos that they recorded over, and then we had all their stems in Delaware Bay. We basically re-recorded everything on top of that again.
"We tried to have just that three-month period to work on it. Any longer than that and we might have gone a bit crazy and deleted the whole thing."
Bartley said his favourite track off the new album was "Honey", while Gallagher chose "Peaches" for its "simplicity and storytelling element".
"In a way [''Honey''] sort of inspired some sort of action out of us," Bartley said.
"We wrote the song in Wellington and it's about wanting to live a lifestyle that we weren't at the time.
"Since then, we've kind of made it happen."
• O and the Mo and will be playing at Lucky Bar with MC Phanny on Saturday, December 5.