Boyle clocked 1:59.05 in a comfortable performance, less than a second outside the qualifying time for Glasgow, finishing clear of the Capital quartet of Samantha Lucie-Smith, Tash Hind, Samantha Lee and Emma Robinson.
The fastest four times tonight also need to go under a combined time of 7:55.92 to qualify a team in the 4x200m freestyle relay.
Stanley clocked 3:53.30 to best heats in the 400m freestyle, just over four seconds outside his best and the qualifying mark.
Snyders, now based in Los Angeles, was impressive with a smooth swim in the 200m breaststroke 2:13.12, less than a second outside the Glasgow mark.
In other swims, USA-based Sophia Batchelor was fastest in heats of the 50m butterfly in 27.19, Otago's Kurt Crosland topped the men's 50m backstroke in 25.75, Caroline Baddock (North Shore) was best in the 200m individual medley heats in 2:20.47 and North Shore's Shaun Burnett topped heats of the 200m butterfly in 1:59.53, less than two seconds outside the qualifying time for Glasgow.
Tonight's finals session starts at 7pm.