There are currently discussions to return to an official paper-based HiSET Testing Center at 1840 Benton St. Santa Clara, CA 95050, and hope to return to in-person paper based testing when possible, given the changing circumstances.
Currently, HiSET is offering online an Exam at Home test option, which offers a great amount of flexibility in scheduling your HiSET exam..
Below, in the first link, are answers to frequently asked questions about the HiSET online test, technical requirements, etc., and the second link, more general information about testing at home through HiSET. What's convenient is testing is available 7 days a week, 15 hours a day, between 4am and 7pm for California testers with the HiSET Exam at Home.