Probably about the same as the classics - around 30 percent. The max is all about fuel savings. Fuel savings look good on a spreadsheet and a quarterly report and can give you instant empirical data.
Our turn times have slowed so much in the last few years, it really isn’t a metric that matters much anymore. As a pilot, I get my part of the turn done in about 5 minutes, shoot the breeze with the A FA, check my phone, use the bathroom, and get food. About 10 prior to push I usually start the apu if I ever turned it off and get ready to go. I am constantly amazed at the huge delays we take, especially at big stations. You can always tell when you are boarding the B group at 5 prior to push and the ops agent looks like someone is holding a gun to their head that things aren’t going well. Then when you are finally ready and the ramp can’t figure out how to get the wireless headset to work for 5 minutes only to tell you that we are waiting on 5 bags, you know it must be go home day. Then when you finally call for push and you are number 3 for the alley, you can text your wife and make a reservation at the commuter hotel.
45 seconds of starting an engine isn’t going to make a hill of beans in this operation. Besides, by that point you are off the gate and nobody at the company cares what happens at that point. They are all about pushing on time no matter what the results at the end of the flight.