He made the remarks during the anti-government rally outside Government House in Bangkok's Phra Nakhon district on Saturday.
The group had earlier gathered at Phan Fa Lilat bridge at 4pm before moving to Government House at 6.30pm.
"It would take three months to eliminate Prayut's regime, not today or tomorrow," he said.
"This regime was made 15 years ago, not seven years. We cannot be patient with Prayut's impudence anymore."
The turnout for the rally on Saturday was low, comparable with Thursday's aborted protest. There was a large police presence.