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)