It isn't just the wait time, but safety. There is less to look out for when turning right vs turning left, resulting in fewer accidents. This is the same reason some employers require employees to back into a parking space when possible.

For me it would also need to know the date because it is reasonable to make a left turn in winter but not in summer.

As I pointed out elsewhere, that's what user preference settings are for, but I'm curious: why the seasonal difference? Snow routes?

Sure. So add a slider to the configuration page: "Avoid left turns when practical."