Can you see Murano, Burarano and Torcello on the same day?
or would it be better to spread over two days?
You can see them in a day.
Yes, one day is fine.
You could see Murano and Torcello in a morning, unless you are into glass Murano can be a short visit,
Murano has two churches that are well worth visiting (San Pietro Martire and Santi Maria e Donato) and a third that is also worth visiting, but it is only open on Sundays (for worship, but you can go in and look around before the service starts). It is a good idea to go straight to Burano and then on to Torcello, as most people will get off the vaporetto at Murano and then go on to Burano and Torcello. By going to Burano first, you may hope to miss the hordes that will arrive later. Then, when you go back to Murano, you can hope that the hordes have left and gone on to Burano. Of course, you could get caught up with the people who get up late, but it's worth a try.
Thanks for the suggestions. Still in the early stages of planning, so lots of reading to be done. Torcello does sound interesting, but we only have two and a half days in Venice. Not even sure if we want to take any out for the islands, but since we don't know if we will ever get back, wouldn't mind spending half a day, but no more.
You should have let us know that in the first place - that you only have 2½ days in Venice. Most of us would have told you that there is so much to see in Venice itself that it is not worth the time it takes to get to Burano, and Torcello, and there is really not enough on Murano to justify a journey there. Although Venice is small, it does take a lot of time to cover, as the only way is on foot - vaporettos don't get you into Venice proper, they only go around the outskirts and along the Grand Canal (and the Cannaregio Canal, if you want to be completely accurate).