The Houston Housing Authority received 20,000 online applications in three hours Monday morning for spots on a waiting list for housing subsidy vouchers. The agency opened the waiting list for the voucher program, commonly known as Section 8, for the first time in six years. It will accept applications, which may only be submitted online, until 11:59 p.m. Sunday. The housing authority will conduct a computer-generated lottery Sept. 3 to select names of about 20,000 people to add to the list. It expects as many as 75,000 applicants, who must meet federal income guidelines to qualify.