The chief executive of Swansea Bay University Health Board said improvements needed to be made after a sharp rise in the number of ambulances stuck outside hospitals.
Tracy Myhill acknowledged that efforts were being made to address the unscheduled care issue but warned at a board meeting: "In the next month or two we need to demonstrate improvements."
Her call followed a report on various performance metrics which revealed that 669 ambulance handovers at Swansea's Morriston Hospital took longer than an hour in April, compared to 380 in April, 2018.
Mrs Myhill, the former chief executive of the Welsh Ambulance Service Trust, said: "Ambulance delays are not going in the right direction, and we need to get a grip on that.
"We all recognise the impact on the community when we are holding up ambulances for whatever reason.
"We have probably got four or five months to get to a significantly better place for the winter."
She added: "The effort is there - it's just the pace of improvement."
Mrs Myhill said the health board was working with the Chief Ambulance Services Commissioner, Stephen Harrhy, on the issue.
Chris White, the health board's chief operating officer, said ambulance handovers were "an immediate priority" for the Welsh Government .
Mr White said spring was feeling "like winter" in terms of pressures at the health board's hospitals. But he hoped the figures for May would show an improvement.
The health board has five priority areas to keep a close eye on - unscheduled care, hospital infections, stroke and cancer care, and planned care - after it was placed in "targeted intervention" by the Welsh Government in 2016.
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It hit half of its targets in these priority areas in April, and missed half.
The report also said there were 4,627 emergency admissions at Morriston, Singleton and Neath Port Talbot hospitals during the month, which was 10% more than April, 2018.
This rise in admissions was in turn a factor in 484 cancelled operations at Morriston Hospital in April.
Mr White said: "We need to create a different type of capacity at Morriston. The key to this is scheduled care."
Martyn Waygood, a non-officer health board member, asked if Neath Port Talbot Hospital could take some of the slack from Morriston.
"Neath Port Talbot has spare capacity (for operations) and wants to take them," he said.
Mr White replied that there could be issues around anaesthetic provision.
The report also said there were, on average, 183 patients at the health board's hospitals who were fit for discharge during April but still occupying beds.
