Convincing western Fairfax County landowners to tax themselves in order to fund the last leg of Dulles Rail is taking longer than expected.

Proponents of establishing a tax district to raise $330 million slipped a self-imposed deadline of Sept. 18 for bringing in the needed signatures from commercial property owners, said attorney Lee Fifer, general counsel for the Western Alliance for Rail to Dulles. The group, said Fifer, needs “a little bit more time.”