Average bandwidth utilization

If you can manage to fit that 24 hour period into one single capture file without crashing Wireshark on loading it you might be able to do that with the I/O graph feature found in the statistics menu.

I kinda expect your line to go way beyond a couple of hundred megabytes though, which usually means you're going to hit the dreaded out of memory wall on loading it again. Maybe capturing only a couple of bytes per frame could drastically reduce the capture file size but you might still encounter memory problems caused by the sheer number of packets you'll record.

Maybe you want to look at other tools instead, like MRTG or something - it's possible they are a better solution for you if you're not interested in capturing packet data but graphing throughput.