COE rejected. When to apply a temporary visa?

Many people I've encountered kept on saying that their temporary visitor visa was rejected because their COE application was previously denied, and that the embassy assumes that they want to change their residence status once they're in Japan. My mother and my clan's alternate plan is to bring me using a temporary visa so that I can visit the place, but a few distant relatives of mine resists against it because of the previous COE rejection.

I don't have any plans to change my residence status but I do have plans to extend my stay to 180 days and apply for a COE once I'm there since my family wants me to overlook at the application myself (since they made the mistake of adding a part-time job plan to my explanation letter and schedule which was the only reason why my COE for dependent visa got denied but miraculously, Japanese Immigration didn't cite my age as another reason even if I'm already an adult).

So I'm pretty much asking here about when I should apply for a temporary visa after a COE rejection. The median I can think of is six months but I've known of people having their temporary visas rejected even when it's been more than that. I tried to contact the Embassy but they never answered my calls. Here's to my brain being well-aware about falsely assuming that my COE needs to be approved before I can even set my foot on Japan.

For those who are curious, The plan is to bring me and my grandmother (if her COE is accepted, she's applying for a long-term resident visa and I'll be applying for a temporary visa simultaneously) to Japan and make her first-generation Japanese so I can be third-generation and thus be eligible for a long-term visa application (My great-grandfather is a second-gen turned first-gen Japanese). My great-great grandfather is pure Japanese by the way.

Please advise passport/country of origin.