Opinions vary, but a moderate degree of proficiency at making basic conversation is consistent, I think, with the attainment of an A2 level (CEFR) in a language. I'd say that's attainable for most with six months of efficient effort if they can commit to full time (or very close to full time) study. "Full time study" obviously translates into a lot more than a single weekly lesson per week.
Also, "efficiency" is key, because some L2 acquisition methods work better than others. Personally I'm a big fan of consuming as much comprehensible input as possible (videos, TV shows, etc). And this time frame, of course, gets longer if one is working a regular job and thus cannot study full time. "One (conversation?) class and a little bit of homework every week" isn't going to move the needle very fast, TBH.