yes you're right. it's nothing far different. in this case "면" has a meaning like "IF" as you mentioned. so 저녁늦게면 아무때나 "could" be considered like, "IF we can meet in the evening, i'm okay on anytime, but if we have to meet in the morning or afternoon, I need to consider" and 저녁늦게 아무때나 "could" be considered like, "I'm free in the evening, other time may not be possible"

저녁 늦게면 아무때나 = anytime (if??) late in the evening This phrase "저녁 늦게면" is incorrect in grammar. The connective ending "-(으)면" must not be attached after adverbs. In my opinion, in the phrase above, the word "저녁 늦게" should be used in direct quotation. I think the speaker leaved out the essential words roughly and excessively. "저녁 늦게" 라면 "저녁 늦게" 라고 (말)한다면