The most important counterargument to address, given that the audience is the city council, would likely be:
Keeping the park open longer would cost the city more money and funds might need to be taken from elsewhere to pay for it.
This is critical because city council members are often concerned with budgetary constraints and resource allocation. Addressing this concern could involve presenting solutions for funding, such as potential partnerships, grants, or community fundraising efforts, which could show that the extended hours can be implemented sustainably without significant financial burden on the city.