So basically I was watching Saiki Kusuo, and something piqued my interest. They wrote 1365 as 一三六五, totally omitting the 千，百，and 十. In this context, it is used to wrote the 1365th time of a meeting. My question is, is this common? In which context is this kind of use acceptable?
Just chiming in to ditto @ItsTokiTime
That said, I’m fairly sure that 一三六五 would still be pronounced せんさんびゃくろくじゅうご, at least in this context (and the context of years or menu prices). Same as we’d read it as “one thousand three hundred and sixty-five” even though we don’t write 1000+300+60+5.
I just talked with several of my co-workers, and the consensus seems to be that there isn’t a hard-and-fast rule about when to use the kanji for 万、千、百、and 十. Generally more kanji = fancier, but the default is whatever is easiest to read. Years (when written in kanji) are usually something like 一一九ニ (1192),
but for a year like 一一一一 (1111) it’s more easy to read written as 千百十一, so some people might write it that way. Addresses generally don’t use 万、千、百、and 十, but an older person or someone writing a very formal letter might choose to write 902-1 as 九百ニ番地１号 (there are about 3 or 4 other more simple ways to write it). Basically, it’s all down to personal preference.