“Technical and practical” issues at the new bus depot in Stockport and the site on Queens Road in north Manchester were to blame for the delays, Mr O’Brien told Radio Manchester.
The Queens Road depot is not expected to be ready to host electric vehicles until the end of 2025, he said, while a date for the Stockport site was currently unknown.
Other updates to the clean air plan include buying fewer electric buses and more diesel buses that are clean-air compliant.
Plans for £5m traffic calming measures on Regent Road in Salford and Quay Street in Manchester city centre are unchanged.
A £30.5m fund to help eligible hackney carriage and private hire vehicles to upgrade to a cleaner vehicle also remains in place.
New data suggests air pollution levels in Greater Manchester are now lower than they were before the pandemic of 2020-21.
Levels of the harmful pollutant nitrogen dioxide breached legal levels in 64 sites across the region, down from 129 sites in 2019, said a combined authority spokesman said.
This was partly due to the city’s investment in cleaner buses after parts of the network were brought back into public control under the Bee Network, he added.
Mr O’Brien said the data was “really encouraging”, and had been achieved without the “hardship to residents and businesses” that a charging clean air zone would cause.
He said local control of public transport also meant authorities could send their greener buses into areas with the worst pollution.
