I’ve had good success with the NBC Sports app. You can watch most events live, or also go back and watch past events.
I agree the times are a bit rough but lots of action going on (T&F at least) between 7pm and 11pm. Also a lot going on early morning. I watched men’s 200m semi finals, women’s 800 and 200 finals, men’s long jump finals and some other stuff live this morning before getting to work.
Having the app on the phone helps… nice to be able to watch while making coffee and breakfast. 
BMX and surfing aren’t my thing, but I’ve watched more of those events than I normally would because they’re in the Olympics. It’s somebody’s thing, so good for those who dedicate themselves to their sports. I’m looking forward to “sport climbing” later this week. Also enjoyed the canoe/kayak slaloms, that’s pretty good action.