Clock times take am, which causes a soft mutation: am ddeg, am ddau. A span uses o... tan. Before and after are cyn and ar ôl, and both are followed by the verb-noun: cyn mynd, ar ôl bwyta.
Examples
- Mae'r apwyntiad am hanner awr wedi deg.
- The appointment is at half past ten.
- Dw i'n gweithio o naw tan bump.
- I work from nine to five.
- Ffonia fi cyn gadael.
- Call me before leaving.
The mistake to avoid
Am causes a soft mutation: am ddeg, not "am deg".
Where this fits in
Cynlluniau a threfniadau, Welsh A2: Cynnig rhywbeth, trefnu ac aildrefnu apwyntiad, a siarad am y tywydd sy'n newid y cynlluniau.