"It is twenty minutes past twelve."
Translation:Mae hi'n ugain munud wedi deuddeg.
The normal spelling is 'ugain' however after the preposition 'ar' if changes to 'hugain'.
In time this applies to
Ugain munud wedi...... and Ugain munud i...** (Twenty past and twenty to)
Pum munud ar hugain wedi...... and Pum munud ar hugain i (literally 'Five minutes on twenty past' and 'Five minutes on twenty to'......)
Hope that clarifies it.