it’s relatively easy to set things up to stream identification sessions. that would give you a record of stream hours, if nothing else.
in a normal “volunteer work” situation, you’d be working with a supervisor who would guide the work and verify your hours. i think the best way to get that kind of formal supervision / verification is to start a club at your school and ask a faculty member to both supervise the club and verify your hours.
otherwise, i think the way you would capture these kinds of efforts is to merely mention them as extracurricular activities, where you would self-report your achievements and time commitment.