Texas is offering a flash sale on August 25th (at 12:01am) for 24 hours. Each individual ticket is $25 and you can specify group seating, which is the inherent advantage of ordering through this process. While buying a ticket on the secondary market may be comparable, it’s less likely to offer that degree of flexibility.
The September 8th kickoff will be at 7:00pm and the sun sets at 7:45pm. Temperatures shouldn’t be a problem.