Seattle city planners on Thursday approved a 27-story apartment tower on First Hill. But a spokesman says the developer, Swedish pension fund Alecta, hasn’t yet decided whether to start building soon or wait.

The 328-unit project would be built at Terry Avenue and Jefferson Street.

Longtime Seattle developer William Justen, who is overseeing the project for Alecta, said the company probably will make a construction decision in the next couple months.

Seattle is in the middle of its biggest apartment-construction boom in more than two decades, and some warn the market is getting overbuilt.

“Is there still time to get in on this cycle?” Justen said. With construction of the tower expected to take 2-1/2 to three years, “it takes a crystal ball,” he added.