Who said anything about being required to wear masks while taking the exam? I am sure the test stations will be physically separated, and actually never considered that Pearson would make people wear masks while testing. Did anyone see this anywhere, or is it just an assumption?
As to OPs question, masks aside, I think the shorter test will be advantageous insofar as we won't have to deal with the wacky field test questions that could cause hang ups in some circumstances, and shorter is always better because it will be less physically draining. No one will have an advantage over anyone else, but it should just be less stressful overall.
Edit: I just found this on the AAMC website. Notice it doesn't say anything about REQUIRING masks!
“This is a rapidly evolving situation, and we thank examinees for their patience. We want to work to ensure the use of safe practices in the test centers,” says Karen Mitchell, PhD, AAMC senior director of admissions testing. Once centers open up, they will practice social distancing measures and rigorous cleaning protocols, and they will allow test-takers to wear gloves and masks.