Thank you, I was thinking about their initial application. Yes, de-orbit times from 550 km are on the order of years to possibly tens of years. The requirement from the FCC is to deorbit your satellite within 25 years after the end of mission.

Edit: Their most recent application only moved the Phase 1 satellites in to the lower orbit. In later phases they are still planning on having more than 1000 satellites at the higher orbital altitude.