Not in Welsh. It is more common in Welsh than in English to change the word order for emphasis - the thing being emphasised - rhan amser, here - is moved to the front of the sentence. This is more or less always done in 'identification' sentences, where the thing being emphasised is someone's name or occupation:

• Dewi yw hwnna - That's Dewi
• Mecanic yw e - He is a mechanic
• Arddwr ydw i - I'm a ploughman

And with other things being emphasised:

• Dim ond rhan amser mae e'n gweithio nawr - He just works part-time now.
• Yn Swyddfa'r Post mae hi'n gweithio nawr, nid yn y llyfrgell - She works in the Post Office now, not in the library.

One major dictionary shows it hyphenated, another has it unhyphenated. Either will do.