She says the minority Liberals need to get through the days of debate the budget motion and bill require before announcing the dates.
But Wynne says she'd rather set the dates before the Aug. 15 deadline.
The two seats in Windsor and London, Ont., were vacated by former cabinet ministers Dwight Duncan and Chris Bentley in February.
The premier says it's just a coincidence that she's visiting both cities this week.
The New Democrats announced Tuesday that they'd support the budget and avoid a provincial election.
Wynne said her schedule was set before she knew what the New Democrats had decided to do. But she remained tight-lipped about when voters in the two ridings may head to the polls.
"I can't pre-empt the process, but if I were a betting person — which I'm not — I'd say we'll want to announce sooner rather than later," she said in Windsor.