Several years ago, before I started my own personal business that requires me to travel all over the Western United States and fly about once a week, I flew occasionally and did not have status. Anytime I booked basic economy, I always waited until 50 minutes before the flight to check in.

I discovered that with basic economy, I was guaranteed to get a bad seat, usually a middle seat, if I checked in 24 hours before the flight. However, if I checked in as late as possible, I often was given an MCE seat for free. This happened at least 50% of the time. My suggestion to anyone on a basic economy ticket is to wait as late as possible to check in. The worst that could happen is you get the bad seat that you would be guaranteed to get if you check in 24 hours before the flight. At best, you'll get main cabin extra for free.