Formula bad after 1 hour or 2 hours?

Do you guys follow the 1 hour rule for tossing formula after baby started bottle or is it okay for 2 hours? My baby likes to takes breaks when she’s having her milk and will rarely drink all at once. So if I make like a 6 ounce bottle, she will have like 3 ounces, take a break of maybe 30 mins or up to an hour or more and then will finish the rest. Sometimes the start to finish will be 2 hours. I hate to toss unfinished formula. I’ve read 2 hours is fine but some people do 1 hour. Which is correct?