I have a lot of stuff in my log file, and it only seems to retain about 10 hours of entries. On at least two occasions, I needed to look at the log for something that happened beyond the scope of the retained log.
Is there any way I can get it to keep 24 hours of data?
Yeah, turn off logging where it's not needed. If you have a device/devices/rules that are hammering the logs then it's going to fill quickly. Unfortunately you're bound to turn something off that you later need for diagnosis - thats the catch. If you need to keep logs for longer then you might be better setting something up to export to Grafana; there are lots of posts on here referring to that.
That would be my suggestion. Setup an external sync of the logs (and any other systems you want) so that you can look through the logs somewhere else without limitations imposed by the Hubitat platform and/or drivers/apps.