I know there are a lot of nouns (especially loanwords like ساعة) that can either be class IX (N/N) or class V (Ji/Ma), and I've never really been clear on the course policy regarding them. However, when I check Wiktionary, it actually claims that when the meaning is specifically "hours" rather than telling time, masaa is the correct term, so I think you should report it.
The way I was taught in Tanzania is that "saa" is in the N/N class and that when people say "masaa" for hours, that is incorrect. That said, I hear lots of people here use "masaa" to mean "hours" contrary to how I was taught. I've even heard people say things like "lisaa limoja" when they're emphasizing that something will only take one hour. At least per my understanding, it just depends whether you are concerned with speaking proper swahili or if you care more about effective communication.