There are some slight sound changes when referring to the dates - days, months, years, hours, and minutes. However it wasn't discussed for the former 4 if the slight sound changes will continue or revert back to normal as it goes on and rotates from 1-10 again. 31 days, 12 months, 12 hours. With span of time, we can surpass this limit. (The usual table used)
So for 34, 44, 54, 64, 74, etc...(ending in 4) Days, should the 4 be pronounced as よっか(かん) or よ(ん) にちかん? For 120, 220, 320, etc...(ending in 20) Days, should the 20 be pronounced as はつかかん or にじゅうにちかん?
How about the 7 and 9 endings? Such as 27 months, 19 hours, and 39/37 days respectively? しち or なな? く or きゅう?
4 endings in hours such as 14,24, etc : always よじかん? 4 endings in months such as 14 months : always し?
Or perhaps both can be used but may sound uncommon or unnatural.
I'm pretty sure that the only slight change for year is 四年 (よねん) and will always continue to be like that. 2004 is にせんよねん.
