I have about 25 gig of hard drive space
That is not a lot. You may want to schedule some disk maintenance, for offloading big files or unused file collections elsewhere.
I have more space on an external drive. If I can use that instead of the main hard drive it would help.
While you can set QuickTime Player to do screen recordings to a pre-defined location, a movie recording would be a temp file on the boot drive, until you save it afterwards.
How many hours of video can I record?
That depends on the recording settings. I think your webcam does 1080p at 30fps, but maybe there are configuration settings to finetune some parameters?
Do a test clip for 5 minutes of “typical content”, i.e. with all the movements and video complexity that is expected for the final run.
Then the resulting file size gives you a good indicator for longer times, as multiples of those 5 minutes.
The 1280×720 camera in my MacBook Pro can record in “Maximum” or “High” quality, meaning using Apple ProRes 422 at ~71.18 Mbps or H.264 AVC at ~10.74 Mbps in my test clip. So, that choice differs in a factor 6.6 for file size as well (2.76 GB vs. 0.42 GB for 5 mins). Not sure if such can apply to your webcam as well.
