Writing numbers

[RebelDogg]

I notice often that Japanese numbers are often written 123... So for the time, it would say １２時２５分 or for the date 10月３１日。。。or is it ３１日１０月。。。I forget. Anyway, the point is that it's not 十月十三日　or　十二時　二十五分。

Is the form using all kanji incorrect or just cumbersome? I ask because I've started incorporating kanji in my flashcards and notes to try to start forcing myself to see and read them. But I don't want to get in the habit of writing my times, dates, or anyother numbers that way if it's incorrect.

Is it just similar to saying 12:25 instead of Twelve Twenty Five?

Thanks!

[QuackingShoe]

Both are correct, but using roman numbers is now more common. It's a lot shorter.
However, often a larger number counter will get thrown into large numbers to break it up like we'd use commas (frequently on the 億, 万 line). Smaller number counters are also sometimes used to cover up 0s, and if the number is high enough that nothing after 億, or nothing after 万, is worth stating, the number will usually end with one or the other. So for example １億７０００万円 and １億７千万円 are both common, but I'd say the former is much more common. The more kanji counters you throw in there, the messier it gets.

[RebelDogg]

Thanks for the response QuackingShoe!

And for the shiney new kanji 億

[Belton]

Style also depends on the context.
In general kanji are preferred when writing top to bottom right to left.
You will also see a fair amount of small shops and restaurants using kanji for prices.
Official documents such as the kouseki (family register) will use kanji not arabic numerals.

off topic
Dates.
It goes from the general (big thing) to the specific (like a lot of constructions in Japanese) so the format is year, month, day. The era system is used a lot instead of the western calender. (2009 is 平成 (heisei) 21) but oddly I've seen signs to remind people what year it is when filling in forms so the western system seems firmly engrained.

[Javizy]

Style also depends on the context.
In general kanji are preferred when writing top to bottom right to left.

Do you mean when writing yourself or something? Most of the novels, books, newspapers, etc, that I own are written in this style, and all of the numbers are written western-style. The impression I get from my friends is that kanji numerals are old-fashioned and difficult to read, whereas up-down right-left books, manga, etc are pretty much standard. In terms of printed materials, I think the same trends are used as with left-right up-down text.

[Belton]

http://www.sljfaq.org/html/yokogaki_and_tategaki.html

Handwritten tategaki (as opposed to typeset). Even extending to numbers of chome etc in addresses. Probably because it looks better or less awkward. Whereas in yokogaki arabic numerals look ok.
More formal writing seems to me to use tategaki and kanji. (wedding cards, funeral cards, new year cards)

That said I've seen kanji used in signage and meishi for phone numbers in both directions. It may just be down to the image they want to project.
It doesn't surprise me that orthography is changing. I can see how arabic numerals would be easier to read or pick out in a large block of text. Nor does it surprise me that aesthetic considerations would be passed over. The thoughts of youth on what is old fashioned would never surprise me though.

Bottom line.
You should be prepared to meet both in reading, (including real world out on the street find your way around reading.)
If you're writing the style is whatever you want it to be.