"It is five minutes to five."
Translation:Mae hi'n bum munud i bump.
Someone else made a similar comment in another conversation. The change in the p at the start of the word is a soft mutation, though.
With the first 5, the soft mutation changes pump to bump. Then the end of bump is dropped to form bum because it's before a noun (bum munud).
The last 5 only has the soft mutation (pump to bump) because it doesn't come before a noun.