Should every minute should be compensated?

I started a job that uses a web-based/AI Clock-in/out timecard.

I already clock in 5-10 minutes early, to get ready and communicate during shift change, so 8.16 hours of work each day and only 8 hours of pay.

I had an instance of needing to actually start my shift 20 minutes early and I clocked in for that start time. When I checked the time card webpage, I only had 15 minutes of additional time.

This happened again with staying over 20 minutes, and only being paid for 15.

I mentioned this to my supervisor with screen shots of my clock-in/out times and the timesheet shorting me 5 minutes.

I'm in CA and wondering what my options are.

For context: last week I read a post in r/jobs mentioned that an interviewer asked them about their willingness to come in on Saturdays (day 6), unpaid. It has been on my mind for a week.

Edits: I recalculated the decimals for the minutes & corrected some spelling.

20 March update: I think it happened again! I am talking with my supervisor. It might just e that the time reporting sister I can access are not showing what payroll is doing. But that means there is no way for me to know if I'm being paid correctly unless the supervisor shares their view of the reporting.