If Amazon is paying people minimum wage, then it could be argued that the extra 30 minutes would push them over the edge of minimum wage laws.
However, from what I recall of Amazon's announcement this year, they pay all warehouse workers at least $15/hr. This means they are significantly above the minimum wage requirement, even if you factor in the 30 minutes spent in security screenings.
In an ideal world, Amazon would factor in the time spent in security screenings, when advertising the job's hourly rate. Ie, workers are spending 5% of their time in security screenings, so the advertised hourly rate should be 5% lower than $15/hr. I would also like for all food-prices in restaurants to factor in taxes for the same reason, but I've thrown the towel on that fight. Ultimately, this seems like a purely cosmetic change with little substance behind it.