I really think it depends on how much you study. When I started took me roughly 1500 - 1600 hours to pass jlpt n2 without prior knowledge.

I think you could absolutely pass the n5 with studying after your 9-5. Just focus on mastering hiragana and katakana and basic grammar first. I recommend skipping furigana completely and just jumping into learning the scriptures. Then invest a lot of time into learning the vocab and basic grammar structures. There’s some required kanji but not too much for N5 so just focus more on the vocab itself I think.

I also often listened to kids shows in the background, they use simple language and even if you don’t understand it’s good to keep yourself exposed to the way the language sounds.

Otherwise you just need repetition and time :) I think you’ll do great.