Lá agus oíche (with a fada).
Scottish also has alternative form là for latha (I believe latha is the default word, là is sometimes used when unstressed). So this phrase could also be là agus oidhche in Sc. Gaelic.
And that is basically the same as pre-Caighdeán Oifigiúil Irish: lá agus oidhche.
Yes, lots of intriguing differences. What's your favourite difference? Which bits are easier or harder? Lack of eclipsis saves an eternity. As I learn Welsh I discover that sometimes when Gaelic differs from Irish it is like Welsh, so presumably the Gaels picked these things up when they arrived in Britain.