Research shows that wearing your mask, and opening the front passenger window, and the window behind the driver seat helps to reduce the spread of the novel coronavirus in your vehicle. See this NY Times article.
I'm a nondriver (vision issues), but the arrangement I have with my current carpoolers (we're always looking for new members!) is that they do all the driving, and I pay for the gas. Everybody seems to feel that this is a "win-win" situation.
As for departure and return hours, there's some flexibility there. We chose the current schedule to try to avoid the commute times with the worst traffic.