You should be very careful about doing this sort of thing, and if you’re disclosing broadcasters subscriber list rather than just caching sub badges that have been in chat, then the broadcaster must be made fully aware your tool will publicise private information.
You don’t need to check every minute, tokens from the code flow last about 4 hours, an the expiry given tells you exactly that.
It’s entirely up to you how you refresh your tokens. Some choose to do it at set intervals using a cronjob or timers, others periodically poll that database for example every 30 minutes and if a token is within x amount of minutes from expiry refresh it, etc…