Overall the percentage of the race shown was 71.23, which is exactly equal to Fox's number at Daytona last week and greater than Fox's number at Sears Point by nearly 3%.
Commercial numbers were similar to Fox, and maybe even slightly less. It may seem like NBC had more commercial minutes though because their breaks are about 30 seconds shorter than on Fox, so they need to run more breaks.
The third hour had 24:00 of commercials, which is the highest number in over two years. That hour alone had 10 breaks, also a record. To be fair to NBC though, they ran four breaks under one caution.