British Transport Police (BTP) constable Jessica Bullough admitted the break, which was supposed to be a maximum of one hour, had been “unacceptable” during Monday’s hearing.
Paul Greaney QC, counsel to the inquiry, said she and a colleague “just missed” Abedi walking into the City Room where he would blow himself up an hour later.
“If you’d come on patrol 10 minutes earlier and if you had seen that man walking in that way, with that bag on his back, would you have regarded him as suspicious?” he asked.
PC Bullough replied that the neighbouring Manchester Victoria railway station frequently contained passengers carrying large items, but added: “Looking at that footage now, if he had walked past me with that bag on his back, I probably would have asked him what was in it.”
CCTV stills were displayed showing PC Bullough and a colleague leaving the station for a kebab just before 7.30pm, then returning 40 minutes later and continuing their break in an office.
She left the station for a cigarette shortly before 9pm, then returned to the office before going back on patrol at 9.36pm.
The hearing was told PC Bullough had been a BTP constable for eight months at the time of the attack, and did not realise that she was the most senior officer on duty that evening.
An email briefing from a senior officer ahead of the Ariana Grande concert said the four BTP personnel on duty were “deployed for the in and out” of fans
“I would like one officer on the concourse close to the barriers, one patrolling the City Room … please can [breaks] be staggered between 19.30 and 21.00 so we have someone at Victoria,” it continued.
PC Bullough admitted that she knew breaks should be taken for between 50 minutes and one hour, and called the length she was away from work “unacceptable”.
The inquiry previously heard evidence from a woman working on an anti-bootlegging operation at the concert, who said she reported Abedi to PC Bullough half an hour before the bombing.
It was played CCTV footage showing what Julie Merchant claims to be an interaction where she told the police officer he was praying, after seeing him “tucked away” and becoming suspicious.
Last week, Ms Merchant said she could not recall if PC Bullough replied but that the police “didn't seem that interested”.
On Monday, PC Bullough said she had no recollection of being approached, having Abedi pointed out to her or being directed to the mezzanine level where he waited for around an hour before blowing himself up.
“I’m confident that they didn’t happen,” she added.
The inquiry heard that PC Bullough had passed a counterterrorism training course three days before the attack on 22 May 2017.
But while being questioned, the officer said she had “no recollection” of the course’s contents.
PC Bullough said she had not been aware of any specific threat to the Grande concert or arena at the time, but that the risk of an attack on departing crowds was “obvious” in hindsight.
When Abedi detonated his bomb at 10.31pm, the officer was standing near a war memorial and no BTP officers had been in the City Room for more than half an hour.
PC Bullough said she believed her position was “one of the best places” to monitor leaving fans, the railway station and traffic outside.
Upon hearing the explosion, she ran straight to the City Room and was the first police officer at the scene of the blast.
PC Bullough provided as much assistance to injured victims as she could, the inquiry heard.
Earlier on Monday, the inquiry heard evidence from a member of the public who said he believed Abedi to be a suicide bomber but thought that security staff were dealing with the risk.
Neil Hatfield, whose four daughters were at the concert, told how he was waiting on the mezzanine level of the City Room with his wife when he noticed a man now known to be Abedi wearing all black and with a large rucksack.
Mr Hatfield said Abedi appeared to be “trying to protect the bag”, but accidentally leaned on it and revealed the contents to be solid.
“If it had been a normal rucksack it would have flexed under his weight but it didn’t,” he told the inquiry.
“It was rock solid and that’s what alarmed me. Alarm bells in my head just went straight away.
“I thought ‘suicide bomber’ straight away, very little doubt in my mind. Honestly my heart was racing as soon as I saw him.”
Mr Hatfield said he had left his phone at home and that his wife was on her phone to their children at the time.
He told how he noticed two nearby security guards, who he believed to be aware of Abedi after thinking one had gestured towards him.
“As far as I was concerned [the security guards] knew he was there, they were talking about him and they were going to do something about it,” he added.
“I was trying to convince myself that it wasn’t a bomber …. I was thinking am I being stupid.”
He described Abedi with “glazed” eyes and said he appeared to be frightened, nervous and agitated.
Sir John Saunders, a retired High Court judge, is leading the probe examining events before, during and after the attack.
In total, 22 victims were killed, 264 people were injured and 710 survivors have reported suffering from psychological trauma.