You can't use the decimal system with the time. 'Un deg dau' = 12 (decimal system), 'deuddeg' = 12 (traditional/vigesimal system).
- un ar ddeg = 11
- deuddeg = 12
- tri ar ddeg = 13
- pedwar ar ddeg = 14
- pymtheg = 15
- un ar bymtheg = 16
- dau ar bymtheg = 17
- deunaw = 18
- pedwar ar bymtheg = 19
- ugain = 20
- un ar hugain = 21 ... and so on. Look at https://en.wikipedia.org/wiki/Welsh_numerals for more info. (Remember to replace dau, tri and pedwar with dwy, tair and pedair with feminine nouns)
Another difference to note is that the noun your're counting comes after the first number in the vigesimal system:
- Decimal: un deg un gath or un deg un o gathod = 'eleven cats'.
- Vigesimal: un gath ar hugain = twenty one cats (literally "one cat on twenty")
So: pum munud ar hugain wedi deuddeg = "twenty five (minutes) past twelve".
The contraction "It's" already means it is, and the solution at the time used the contraction and then the full word is, effectively saying in english "It is is" while as far as I'm aware no dialect of english doubles the word 'is' like that.
It's a subtle typo, I had to look at my own quote for like a whole minute before I remembered what was wrong lol
When telling the time we use the twelve hours.
- deuddeg o'r gloch - twelve o'clock (could be midday or midnight)
- hanner dydd/nos - midday/midnight specifically
24 hours ( eg, 'fifteen thirty-five') is used when reading out timetables, etc, which are written using the 24-hour clock.