I don't expect this is particularly important, but I want to get it right if there is a correct method.

When writing dates in dialogue should they be given in number form or word form (i.e. two-thousand-and-twenty or, just, 2020). Also, if written in words should the words be connected with "-" for ease of reading? Or, as I think I've heard somewhere are "-" one of those things to try and avoid?

The reason I ask is because in radio scripts I know it's written in words, however film scripts seem to hold a whole bunch of new and different rules.

Cheers,
Alex

In dialogue, you spell it out.

The reason you will want to always write out any number that you have is because numbers can be said a variety of different ways. 2020, for example.

It could be:
twenty twenty -or- two thousand twenty -or- two thousand and twenty -or- two zero two zero -or- twenty hundred twenty

The conbinations are endless and it is all based on usage and vernacular. I would never say two thousand and twenty, for example, because I just don't talk that way. As a screenwriter, you might have a character who does, though.

And dashes should only be used in their proper English context: two combine tens and ones places for numbers between twenty and one hundred (i.e. twenty-one or eighty-seven)